DE102019210450A1 - Optical diffraction component for the suppression of at least one target wavelength through destructive interference - Google Patents

Abstract

An optical diffraction component (60) is used to suppress at least one target wavelength by destructive interference. The diffractive optical component (60) has at least three diffraction structure levels (N1, N2, N3, N4). The diffraction structure levels (N1, N2, N3, N4) can be assigned to at least two diffraction structure groups. A first of the diffraction structure groups (35) is used to suppress a first target wavelength λ1. A second of the diffraction structure groups is used to suppress a second target wavelength λ2. The following applies to the two target wavelengths λ1 and λ2: (λ1- λ2) 2 / (λ1 + λ2) 2 <20%. A topography of the diffraction structure levels (N1 to N4) can be described as a superposition of two binary diffraction structure groups. Boundary areas (N3 / N1, N2 / N4, N4 / N3, N1 / N2) between adjacent surface sections of each of the binary diffraction structure groups have a linear course and overlap at most along sections of the linear course. In a variant of the optical diffraction component, the arrangement of the diffraction structures is such that a wavelength range around a first target wavelength λ1 in the infrared wavelength range, which is diffracted by a periodic grating structure profile, has radiation components with at least three different phases that destructively interfere with one another . The diffraction structure levels have a neutral diffraction structure level, a positive diffraction structure level and a negative diffraction structure level. The result is an optical diffraction component, the possibilities of which are expanded, in particular for suppressing false light.

Description

The invention relates to an optical diffraction component for suppressing at least one target wavelength by destructive interference. The invention also relates to an EUV collector of a projection exposure system with such an optical diffraction component, an illumination system with such an EUV collector, an optical system with such an illumination system, a projection exposure system with such an optical system, and a method for producing a structured component with the aid such a projection exposure system and a structured component produced in this way.

An EUV collector with an optical diffraction component in the form of an optical grating is known from US Pat WO 2017/207401 A1 and from the WO 2014/114405 A2 . Designs of optical gratings for suppressing IR wavelengths in EUV projection exposure systems are known from the publication "Multilayer EUV optics with integrated IR suppression gratings", T. Feigl et al., 2016 EUVL Workshop, Berkeley, June 13-16, 2016 . The EP 1 540 423 B1 describes a grating-based spectral filter for suppressing radiation outside a useful band in an EUV lithography system. The US 2014/0131586 A1 describes a phase grating for a mask inspection system. The DE 10 2009 044 462 A1 describes an optical filter element with a grid structure for the diffraction of infrared radiation within an EUV lighting system. The specialist article "Multilevel blazed gratings in resonance domain: an alternative to the classical fabrication approach" by M. Oliva et al., OPTICS EXPRESS, Vol. 19, No. 15, 2011, pp. 1473 to 1475 and the specialist article "Highly efficient three-level blazed grating in the resonance domain" by M. Oliva et al., OPTICS LETTERS Vol. 35, No. 16, 2010, pp. 2774 to 2776 describe different variants of blaze grids. From the specialist article "Diffractive elements designed to suppress unwanted zeroth order due to surface depth error" by V. Kettunen et al., Journal of Modern Optics 51, 14, 2111-2123, 2004 diffractive elements for suppressing undesired zeroth diffraction orders due to a profile depth error are known.

An optical grating can be used to suppress stray light with a wavelength that differs from useful light. The stray light can then be diffracted by the optical grating towards a light trap (beam dump), whereas useful light takes a different path.

It is an object of the present invention to develop an optical diffraction component of the type mentioned at the beginning in such a way that its possible uses are expanded, in particular for suppressing false light.

This object is achieved according to the invention by an optical diffraction component with the features specified in claim 1.

By using an optical diffraction component with at least three diffraction structure levels, which in turn can be assigned to at least two diffraction structure groups that serve to suppress respective target wavelengths that are not too far apart, there is surprisingly an improvement in the suppression of the target wavelength, which goes well beyond the suppression effect of the individual diffraction structure groups. In comparison to optical diffraction components of the prior art, there are degrees of design freedom which can be used to make the possible uses of the optical diffraction component more flexible. The different diffraction structure groups can occupy the same optically used area of the optical diffraction component, so do not have to be arranged on sections that are separate from one another on this optically used area. The optical diffraction component can in particular be designed so that the two diffraction structure groups are designed to suppress the same target wavelength or false light wavelength. Alternatively or additionally, the optical diffraction component can be designed to suppress several target wavelengths with a corresponding design of the diffraction structure groups. In the case of such an optical diffraction component having a plurality of diffraction structure groups, it has been found that a diffractive effect is improved in comparison with an optical diffraction component with precisely one diffraction structure group. The same suppressive effect can be achieved when using the optical diffraction component with several diffraction structure groups, that is, with manufacturing tolerances that are relaxed compared to the prior art.

For the upper limit, which characterizes the difference between the two target wavelengths, the following can apply: (λ ₁ - λ ₂ ) ² / (λ ₁ + λ ₂ ) ² <10%, <5%, <2%, <1 %, <0.5%, <0.2%, <0.1% or even <0.05%. The two target wavelengths produced by the at least two diffraction structure groups of the optical Diffraction components are suppressed can be exactly the same. A deviation (λ ₁ - λ ₂ ) ² / (λ ₁ + λ ₂ ) ² , which characterizes the difference between the two target wavelengths, can be greater than 0.2%, can be greater than 0.5% be greater than 0.7% and can be even greater.

The target wavelengths can be in the IR wavelength range, for example in the range of the typical emission wavelengths of CO ₂ lasers at 10.6 μm. Alternatively or additionally, wavelengths in the NIR wavelength range in the visible wavelength range, in the UV wavelength range or also in the DUV wavelength range can represent target wavelengths to be suppressed. One of the two target wavelengths can be 10.2 µm and the other of the two target wavelengths can be 10.6 µm. The target wavelengths can be adapted to the wavelengths of a prepulse and a main pulse of an EUV plasma light source.

Due to the design of the at least two diffraction structure groups for the suppression of two different target wavelengths, there is a suppression of wavelengths within a predefinable wavelength bandwidth, which can also be referred to as the suppression design bandwidth. Wavelengths that lie within this suppression design bandwidth, i.e. which can be effectively suppressed with the optical diffraction component, can correspond to the target wavelengths and / or can lie between the target wavelengths and / or can be outside a wavelength range between the target Wavelengths lie. To suppress a wavelength of 10.2 µm, for example, a first target wavelength, for which the first of the diffraction structure group is designed, at 10.25 µm and a second target wavelength, for which the second diffraction structure group is designed, are 10.55 µm. The selection of the target wavelengths depends on the requirements that are placed on the optical diffraction component for suppressing, if necessary, a plurality of different wavelengths or wavelength bandwidths. A position of further minima of a destructive interference in addition to the target wavelengths can also be taken into account, or it can be taken into account which wavelengths are specifically not to be suppressed.

The optical diffraction component can have exactly three diffraction structure levels and can have exactly two diffraction structure groups. Alternatively, the optical diffraction component can also have more than three diffraction structure levels, for example four, five, six, or even more diffraction structure levels, and accordingly also more than two diffraction structure groups.

A binary structure is a structure with positive structures ("mountains") and negative structures ("valleys"), whereby the total area of the positive structures corresponds to the total area of the negative structures within specified tolerances. A difference between the total areas of the positive structures on the one hand and the negative structures on the other hand can be smaller than 20%, can be smaller than 10%, can be smaller than 5%, can be smaller than 2% and can also be smaller than 1%. The total areas can also be exactly the same.

Because the boundary areas of the first and the second binary structure overlap each other at most along sections of the linear course of the boundary areas, there is the possibility of producing the optical diffraction component with the aid of comparatively simply designed lithographic mask structures. There is the possibility of a precise production of the optical diffraction component while maintaining tight tolerances for the surfaces of the diffraction structure levels on the one hand and also for their structure depths on the other hand. In particular, diffraction structure groups with a desired large and desired precise edge steepness of the border areas can be generated.

The optical diffraction component can be designed in such a way that a rising limit area, that is to say a rising level flank, is assigned a falling limit area with the same structure depth, that is to say the same structure height difference.

In the case of a completely separated course of the boundary regions according to claim 2, there is a further simplification in particular of a lithographic production of the optical diffraction component.

With regard to the embodiment according to claim 3, the use of an optical grating with at least two diffraction gratings with fundamentally independent grating periods and fundamentally independent structure depths result, with at least one of the diffraction gratings the structure depth being small compared to the grating period, compared to optical gratings of the State of the art Design degrees of freedom that can be used to make the possible uses of the optical grating more flexible. The two diffraction gratings can occupy the same grating area, so they are not on the grating area arranged on separate sections. The two diffraction gratings are then superimposed on one another on the grating surface. The optical grating can be designed in such a way that its false light suppression is improved by designing the two diffraction gratings to suppress the same false light wavelengths. As an alternative or in addition, the optical grating can be designed in such a way that several stray light wavelengths can be suppressed. Surprisingly, it has also been found that when using such an optical grating having multiple diffraction gratings, a diffractive effect, in particular a suppressing effect through destructive interference in the zeroth diffraction order, is improved compared to an optical grating with exactly one diffraction grating. The same suppressive effect can therefore be achieved when using the optical grating with several diffraction gratings with relaxed manufacturing tolerances.

The optical grating can be designed as a reflection grating, but can alternatively also be designed as a transmission grating and, for example, as a phase grating.

The grid surface can be flat or curved, e.g. B. convex or concave. The grating surface can be part of an optical surface of an optical component, which additionally has another optical function, for example on a beam collector or a mirror. The first diffraction grating and / or the second diffraction grating can be designed as a binary grating or binary grating in which an area of the positive structures is equal to an area of the negative structures. In the simplest case, the structure depth can be the difference in height between the respective positive diffraction structures and the associated negative diffraction structures.

The optical grating can also have a highly reflective layer and, if necessary, auxiliary layers, in particular to protect the optical grating and / or the highly reflective layer. The highly reflective layer can be designed as a multilayer layer. The highly reflective layer can be designed for EUV light in a wavelength range in particular between 5 nm and 30 nm.

The optical diffraction component can be designed as a multi-stage diffraction grating with correspondingly arranged diffraction structure levels.

A structure depth can be one sixth of the target wavelength. With a corresponding design of the multi-level grating, a structure depth can also be a quarter of the target wavelength.

Depending on a number m of the different diffraction structure levels, a structure depth depending on the target wavelength λ _{N can} be: b = λ _N / (2m).

A grating period can be in the range of millimeters and can be, for example, 1 mm or 2 mm.

The diffraction structure levels can be designed as flat surfaces.

The grating periods of the various diffraction gratings can have an integer ratio to one another. The grating periods can have a defined phase offset from one another.

A ratio of the grating periods can be 1: 2. When using three diffraction gratings, the ratio of the grating periods can be 1: 2: 4 or 1: 2: 2.

An area ratio of areas of the first positive diffraction structures to areas of the first negative diffraction structures can be in the range between 0.9 and 1.1. An area ratio of areas of the second positive diffraction structures to areas of the second negative diffraction structures can be in the range between 0.9 and 1.1. Correspondingly precise binary diffraction structure groups result.

A ratio between the first grating period and the first structure depth can be greater than 10. A ratio between the second grating period and the second structure depth can be greater than 10.

There are correspondingly different target wavelengths to be suppressed. In addition to the two target wavelengths λ ₁ and λ ₂ , a further, more strongly deviating target wavelength can thus be suppressed. For example, it is possible to suppress different target wavelengths in the infrared wavelength range and a further target wavelength in the ultraviolet wavelength range at the same time.

A period ratio of the first grating period to the second grating period can be in the range between 0.9 and 1.1.

The advantages of an optical diffraction component according to claim 6 enable, given good reflection conditions, especially for EUV wavelengths, good false light suppression of higher wavelengths even with the second diffraction grating.

An optical diffraction component with a period ratio according to claim 7 can be manufactured well. The grating periods of the first and the second diffraction grating can be exactly the same, but can also be different.

A structure depth ratio of the structure depth of the first diffraction grating to the structure depth of the second diffraction grating can be in the range between 0.9 and 1.1. The structural depths of the first and the second diffraction grating can be different from one another, but can also be the same. A significantly larger structure depth ratio between the two diffraction gratings in the range between 1.1 and 20 is also possible, for example a structure depth ratio in the range of 10.

An optical diffraction component according to Claim 4, in which the period running directions of the first and second diffraction gratings do not run parallel to one another, has proven useful. A smallest angle between the period running directions can be 90 °, so that the two period running directions are perpendicular to one another. A smaller, smallest angle, for example in the range of 60 °, 55 °, 45 ° or 30 ° is possible.

Alternatively, an embodiment of the optical diffraction component is also possible in which the two period running directions of the at least two diffraction structure groups run parallel to one another.

In the case of an optical diffraction component with at least one further diffraction grating according to claim 5, there is a corresponding further increase in the degrees of freedom of design available. At least two of the period running directions of the at least three diffraction gratings can have mutually different directions. Alternatively, it is also possible that all period directions of the at least three diffraction gratings run parallel to one another.

The advantages of the optical diffraction component according to claim 6 correspond to those which have already been explained above. The grating periods of the first diffraction grating and of the further diffraction grating can be the same, but can also be different. Corresponding period ratios in the range between 0.9 and 1.1 or the same grating periods can also be present between the second diffraction grating and the at least one further diffraction grating.

A structure depth ratio of the first diffraction grating to the further diffraction grating can be in the range between 0.9 and 1.1, structure depths of the first and the further diffraction grating can be different from one another, but can also be the same. Corresponding structural depth ratios in the range between 0.9 and 1.1 or even the same structural depth can also be present between the second diffraction grating and the at least one further diffraction grating. A significantly larger structure depth ratio between the structure depths of the further diffraction grating and the first and / or second diffraction grating in the range between 1.1 and 20, for example in the range of 10, is possible.

A smallest angle between the period running directions of the first diffraction grating and the further diffraction grating can be in the range between 20 ° and 25 °. Another smallest angle z. B. in the range between 10 ° and 80 ° is possible. Corresponding running direction angles can also be present between a period running direction of the second diffraction grating and the period running direction of the at least one further diffraction grating.

In particular, binary grids for the different diffraction structure groups of the optical diffraction component result in the same area contributions according to claim 7. This ensures a high level of false light suppression in the area of the zeroth diffraction order with a corresponding design of the optical diffraction component.

The object mentioned at the beginning is also achieved by an optical diffraction component with the features mentioned in claim 8.

A range to be suppressed around the target wavelength λ ₁ can be selected so that several wavelengths to be suppressed are detected, for example the different wavelengths of a prepulse and a main pulse of an EUV plasma light source.

According to claim 8, the positive diffractive structure level on the one hand and the negative diffraction structure level on the other hand designed with a tolerance range of at most 20% to the optical path length of λ _1/4 with respect to the neutral diffraction structure level. This tolerance as compared to the path length λ _1/4 may be also lower than +/- 20% and may, for example, +/- 10%, +/- 5%, +/- 3%, +/- 2%, or even + / - 1%.

The diffractive optical component according to claim 8 can additionally have features which have already been discussed above with reference to the diffractive optical component according to the preceding claims.

In the embodiment of the optical diffraction component according to claim 9, the two neutral diffraction structure levels can be arranged separated from one another by a positive diffraction structure level or by a negative diffraction structure level in the grating period. Alternatively, the two neutral diffraction structure levels can also be arranged in direct succession in the grating period as a neutral diffraction structure level of double length.

In the case of an optical diffraction component according to claim 10, a particularly good destructive interfering suppressing effect results for the target wavelength. The lengths of the four period segments can differ from one another by less than 20%, for example by less than 15%, by less than 10%, by less than 5%, by less than 2% or also by less than 1%. The lengths of the four period segments can also be exactly the same.

A sequence of period segments according to claim 11 has proven to be particularly suitable. A corresponding sequence can be achieved by cyclically interchanging the sequence specified in claim 11, resulting in the following sequence, for example: neutral diffraction structure level, positive diffraction structure level, neutral diffraction structure level, negative diffraction structure level.

The following sequence of the four periods is also possible: negative diffraction structure level, neutral diffraction structure level, positive diffraction structure level, neutral diffraction structure level. A cyclical exchange is also possible with this variant.

As a further variant of the sequence of the four period segments, the following can be used: neutral diffraction structure level, neutral diffraction structure level; Positive diffraction structure level, negative diffraction structure level. So here there are two neutral diffraction structure levels directly next to each other as a common neutral diffraction structure level, in particular of double length. In this variant too, a z. B. cyclical swapping possible.

The advantages of the optical diffraction component according to claim 12 correspond to those which have already been explained above. It also applies to the second target wavelength λ ₂ that this is weakened or suppressed by destructive interference due to a corresponding design of diffraction structures of the optical diffraction component. For the selection of the target wavelengths λ ₁ and λ ₂ , what has already been discussed above in connection with the optical diffraction component according to the preceding claims can apply.

The advantages of an EUV collector or an EUV collector mirror according to claim 13 correspond to those that have already been explained above with reference to the optical diffraction component. These advantages are particularly evident when used in conjunction with an EUV light source, in which plasma is generated by laser-induced discharge.

This applies in particular to an EUV collector mirror according to claim 14. The radiation of the at least one target wavelength is also referred to as false light.

The advantages of a lighting system according to claim 15 correspond to those which have already been explained above with reference to the EUV collector according to the invention. The EUV useful light is not suppressed by the optical diffraction component, so it has a different wavelength than the false light to be suppressed.

The lighting system can be designed with the optical diffraction component implemented as described above in such a way that a homogeneous distribution of the false light takes place in the area of false light discharge locations and for example in the area of beam dumps provided for this purpose. As an alternative or in addition, a predetermined distribution function of the useful light can be ensured, in particular in specific sections of an illumination beam path of the illumination system, for example in the area of a pupil plane.

The advantages of an optical system according to claim 16, a projection exposure system according to claim 17, a manufacturing method according to claim 19 and a micro- or nano-structured component according to claim 20 correspond to those already explained above with reference to the collector according to the invention.

Differences between the wavelengths of the prepulse light on the one hand and the main pulse light on the other hand in the case of the pump light source of the EUV light source of the projection exposure system according to claim 18 can have upper or lower limit values, which have already been explained above in connection with the target wavelengths λ ₁ and λ ₂ .

In particular, a semiconductor component, for example a memory chip, can be produced with the projection exposure system.

• 1 schematisch eine Projektionsbelichtungsanlage für die EUV-Mikrolithographie;
• 2 Details einer Lichtquelle der Projektionsbelichtungsanlage im Umfeld eines EUV-Kollektors zur Führung von EUV-Nutzlicht von einem Plasma-Quellbereich hin zu einem Feldfacettenspiegel einer Beleuchtungsoptik der Projektionsbelichtungsanlage, wobei der EUV-Kollektor in einem Meridionalschnitt dargestellt ist;
• 3 in einer im Vergleich zur 3 abstrakteren Darstellung eine Führung einerseits von EUV-Nutzlicht und andererseits von wellenlängenverschiedenen Falschlicht-Anteilen bei einer Reflexion/Beugung am EUV-Kollektor;
• 4 eine Aufsicht auf einen Abschnitt einer Gitterfläche eines optischen Gitters mit zwei Beugungsgittern als Beugungs-Strukturgruppen mit aufeinander senkrecht stehenden Perioden-Laufrichtungen und gleichen Gitterperioden, wobei drei Beugungsstruktur-Niveaus vorgebende Strukturtiefen von in der 4 quadratischen Beugungsstrukturen über verschiedene Schraffurtypen veranschaulicht sind, wobei das optische Gitter eine Ausführung einer optischen Beugungskomponente zur Unterdrückung mindestens einer Ziel-Wellenlänge durch destruktive Interferenz darstellt;
• 5 in einem Diagramm eine wellenlängenabhängige Reflektivität R des optischen Gitters nach 4 für einen berechneten Idealfall und für einen weiteren, berechneten, realitätsnäheren Fall sowie für ein nicht erfindungsgemäßes Referenzgitter, wobei die beiden Beugungsgitter des optischen Gitters zur Unterdrückung zweier verschiedener Wellenlängen ausgeführt sind;
• 6 in einem zu 5 ähnlichen Diagramm die Verhältnisse bei einem optischen Gitter nach 4, wobei die beiden Beugungsgitter identische Strukturtiefen haben, sodass das optische Gitter zur Unterdrückung genau einer Wellenlänge ausgeführt ist;
• 7 in einer zu 4 ähnlichen Darstellung eine weitere Ausführung eines optischen Gitters mit zwei Beugungsgittern als Beugungs-Strukturgruppen mit Perioden-Laufrichtungen, die zueinander einen Winkel von 45° einnehmen, wobei das optische Gitter eine Ausführung einer optischen Beugungskomponente zur Unterdrückung mindestens einer Ziel-Wellenlänge durch destruktive Interferenz darstellt;
• 8 in einer zu den 4 und 7 ähnlichen Darstellung eine weitere Ausführung eines optischen Gitters mit drei Beugungsgittern als Beugungs-Strukturgruppen, von denen zwei Perioden-Laufrichtungen haben, die aufeinander senkrecht stehen, und ein drittes Beugungsgitter eine hierzu diagonale Perioden-Laufrichtung aufweist, wobei das optische Gitter eine Ausführung einer optischen Beugungskomponente zur Unterdrückung mindestens einer Ziel-Wellenlänge durch destruktive Interferenz darstellt;
• 9 in einem zu den 5 und 6 ähnlichen Diagramm Reflexionsverhältnisse bei einem optischen Gitter nach 8, bei dem alle drei Beugungsgitter zur Unterdrückung ein und derselben Wellenlänge ausgeführt sind;
• 10 in einem zu 9 ähnlichen Diagramm die Reflexionsverhältnisse bei einem optischen Gitter nach Art der 8, wobei die drei Beugungsgitter verschiedene Strukturtiefen aufweisen, sodass das optische Gitter zur Unterdrückung verschiedener Wellenlängen ausgeführt ist;
• 11 in einer zu 8 ähnlichen Darstellung eine weitere Ausführung eines optischen Gitters mit drei Beugungsgittern als Beugungs-Strukturgruppen mit jeweiligen Perioden-Laufrichtungen, die paarweise einen von null verschiedenen Winkel einnehmen, wobei das optische Gitter eine Ausführung einer optischen Beugungskomponente zur Unterdrückung mindestens einer Ziel-Wellenlänge durch destruktive Interferenz darstellt;
• 12 und 13 in einer zu 11 ähnlichen Darstellung weitere Ausführungen von optischen Gittern mit jeweils drei Beugungsgittern als Beugungs-Strukturgruppen mit Perioden-Laufrichtungen entsprechend denen der Ausführung nach 11, wobei die Beugungsstrukturen der Ausführungen nach den 12 und 13 zueinander und in Bezug auf die Ausführung nach 11 in der jeweiligen Perioden-Laufrichtung versetzt angeordnet sind, wobei die optischen Gitter weitere Ausführungen von optischen Beugungskomponenten zur Unterdrückung mindestens einer Ziel-Wellenlänge durch destruktive Interferenz darstellen;
• 14 in einer Seitenansicht eine erste Beugungs-Strukturgruppe, die zu einer weiteren Ausführung einer optischen Beugungskomponente zur Unterdrückung mindestens einer Ziel-Wellenlänge durch destruktive Interferenz gehört, ausgeführt als Binärgitter mit einer ersten Gitterperiode und einer ersten Strukturtiefe;
• 15 in einer zu 14 ähnlichen Darstellung eine weitere Beugungs-Strukturgruppe als Bestandteil der optischen Beugungskomponente, wobei die weitere Beugungs-Strukturgruppe wiederum als Binärgitter mit einer Gitterperiode und einer Strukturtiefe ausgeführt ist, wobei zudem gestrichelt ein möglicher Overlay-Fehler bei der Herstellung dieser Beugungs-Strukturgruppe angedeutet ist;
• 16 die sich als Überlagerung der beiden Beugungs-Strukturgruppen nach den 14 und 15 ergebende optische Beugungskomponente;
• 17 bis 19 in zu den 14 bis 16 ähnlichen Darstellungen zwei Beugungs-Strukturgruppen sowie die sich hieraus durch Überlagerung ergebende weitere optische Beugungskomponente;
• 20 bis 22 in zu den 14 bis 16 ähnlichen Darstellungen zwei Beugungs-Strukturgruppen sowie die sich hieraus durch Überlagerung ergebende weitere optische Beugungskomponente;
• 23 in einem Diagramm eine Reflektivität einer optischen Beugungskomponente nach Art derjenigen der 16, 19 oder 22, wobei die Strukturhöhe der jeweils ersten Beugungs-Strukturgruppe auf einem Wert zur Unterdrückung einer Ziel-Wellenlänge festgehalten ist und die Reflektivität in Abhängigkeit von der Strukturhöhe der anderen Beugungs-Strukturgruppe aufgetragen ist;
• 24 wiederum in einem Diagramm die Reflektivität der optischen Beugungskomponente, wiederum bei festgehaltener Strukturtiefe der ersten Beugungs-Strukturgruppe, aufgetragen als Funktion eines Unterschiedes der Strukturtiefen der beiden Beugungs-Strukturgruppen und normiert auf die Strukturtiefe der ersten Beugungs-Strukturgruppe;
• 25 in einer zur 14 ähnlichen Darstellung eine Beugungs-Strukturgruppe, ausgeführt als Binärgitter mit einer Gitterperiode und einer Strukturtiefe, als Bestandteil einer durch Überlagerung von drei Beugungs-Strukturgruppen entstehenden weiteren Ausführungsform einer optischen Beugungskomponente zur Unterdrückung mindestens einer Ziel-Wellenlänge durch destruktive Interferenz;
• 26 eine weitere, wiederum als Binärgitter ausgeführte Beugungs-Strukturgruppe zur Ausbildung dieser Variante der optischen Beugungskomponente;
• 27 eine weitere, wiederum als Binärgitter ausgeführte Beugungs-Strukturgruppe zur Ausbildung dieser Variante der optischen Beugungskomponente;
• 28 die optische Beugungskomponente, gebildet als Überlagerung der drei Beugungs-Strukturgruppen nach den 25 bis 27;
• 29 bis 32 in zu den 25 bis 28 ähnlicher Darstellung drei Beugungs-Strukturgruppen, wiederum jeweils ausgeführt als Binärgitter mit einer Gitterperiode und einer Strukturtiefe, sowie eine sich hieraus durch Überlagerung ergebende weitere Ausführung einer optischen Beugungskomponente zur Unterdrückung mindestens einer Ziel-Wellenlänge durch destruktive Interferenz.
• 33 in einem zu den 9 und 10 ähnlichen Diagramm wellenlängenabhängige Reflexionsverhältnisse bei optischen Beugungskomponenten nach Art derjenigen nach einer der 8, 11 bis 13, 28 oder 32, wobei die Beugungs-Strukturgruppen verschiedene Strukturtiefen aufweisen, sodass das optische Gitter zur Unterdrückung verschiedener, im Vergleich zur Variante nach 10 aber näher beieinander liegender Wellenlängen ausgeführt ist;
• 34 in einer zu 4 ähnlichen Darstellung einen Abschnitt einer Gitterfläche eines optischen Gitters mit drei Beugungsgittern als Beugungs-Strukturgruppen, wobei zwei der Gitter parallele Perioden-Laufrichtungen aufweisen und ein drittes Gitter eine hierauf senkrecht stehende Perioden-Laufrichtung aufweist und wobei die Beugungs-Strukturgruppen mit gleicher Perioden-Laufrichtung nach Art der Ausführung nach den 16, 19 oder 22 überlagern, wobei Strukturtiefen von in der 34 rechteckigen Beugungsstrukturen über verschiedene Schraffurtypen veranschaulicht sind, als weitere Ausführung einer optischen Beugungskomponente zur Unterdrückung mindestens einer Ziel-Wellenlänge durch destruktive Interferenz;
• 35 eine weitere Ausführung einer optischen Beugungskomponente zur Unterdrückung mindestens einer Ziel-Wellenlänge durch destruktive Interferenz, ausgeführt als Dreistufen-Gitter, ausgeführt zur Unterdrückung genau einer Ziel-Wellenlänge, wiederum in einer schematischen Seitenansicht;
• 36 in einer zu 35 ähnlichen Darstellung eine weitere Ausführung einer optischen Beugungskomponente zur Unterdrückung mindestens einer Ziel-Wellenlänge durch destruktive Interferenz, wiederum gestaltet mit drei Beugungsstruktur-Niveaus, die zwei Beugungs-Strukturgruppen zuordenbar sind, wobei Größen eingezeichnet sind, die zur theoretischen Beschreibung einer Berechnung einer Unterdrückungs-Effizienz der mindestens einen Ziel-Wellenlänge eingezeichnet sind;
• 37 in einer zu den 35 und 36 ähnlichen Darstellung eine weitere Ausführung einer optischen Beugungskomponente zur Unterdrückung mindestens einer Ziel-Wellenlänge durch destruktive Interferenz, ausgeführt mit vier Beugungsstruktur-Niveaus, die einer entsprechenden Mehrzahl von Beugungs-Strukturgruppen zuordenbar sind;
• 38 und 39 in zu 37 ähnlichen Darstellungen zwei weitere Ausführungen von optischen Beugungskomponenten zur Unterdrückung mindestens einer Ziel-Wellenlänge durch destruktive Interferenz, ausgeführt mit wiederum vier Beugungsstruktur-Niveaus;
• 40 in einem Diagramm eine wellenlängenabhängige Reflektivität einer optischen Beugungskomponente mit zwei Beugungs-Strukturgruppen nach Art beispielsweise der Ausführungen nach den 4, 7, 16, 19, 22, 35, 36, wobei die beiden Beugungs-Strukturgruppen mit Strukturtiefen zur Unterdrückung zweier DUV-Wellenlängen ausgeführt sind;
• 41 in einer zu 40 ähnlichen Darstellung eine wellenlängenabhängige Reflektivität für eine optische Beugungskomponente mit insgesamt fünf Beugungsstruktur-Niveaus, denen vier Beugungs-Strukturgruppen mit unterschiedlichen Strukturtiefen zuordenbar sind, wobei zwei Ziel-Wellenlängen im IR-Bereich oberhalb von 10 µm und zwei Ziel-Wellenlängen im DUV-Bereich vergleichbar zu den Ziel-Wellenlängen nach 40 unterdrückt werden;
• 42 eine Ausschnittsvergrößerung aus 41 im DUV-Bereich zwischen 0,1 µm und 0,4 µm;
• 43 wiederum in einem Diagramm eine wellenlängenabhängige Reflektivität zwischen 10,0 µm und 11,0 µm für verschiedene optische Beugungskomponenten mit unterschiedlicher Flankensteilheits-Toleranz der Beugungs-Strukturgruppen;
• 44 die optische Beugungskomponente nach 16 zusammen mit zwei lithographischen Maskenstrukturen, die bei der Herstellung der optischen Beugungskomponente zur Vorgabe von Grenzbereichen zwischen benachbarten Flächenabschnitten einander überlagernder binärer Strukturen der optischen Beugungskomponente genutzt werden können;
• 45 in einer zu 44 ähnlichen Darstellung die optische Beugungskomponente nach 19 zusammen mit zwei lithographischen Maskenstrukturen, die bei der Herstellung der optischen Beugungskomponente zur Vorgabe wiederum der Grenzbereiche zwischen den Flächenabschnitten der Beugungs-Strukturgruppen genutzt werden können;
• 46 eine weitere Ausführung einer optischen Beugungskomponente zur Unterdrückung mindestens einer Ziel-Wellenlänge durch destruktive Interferenz mit einem periodischen Gitter-Strukturprofil mit Beugungs-Strukturen, die drei Beugungsstruktur-Niveaus aufweisen, die derart angeordnet sind, dass die Ziel-Wellenlänge durch destruktive Interferenz unterdrückt wird;
• 47 die optische Beugungskomponente nach 46, wobei die drei Beugungsstruktur-Niveaus einen Höhen- bzw. Niveauunterschied zueinander aufweisen, der zu einer perfekten destruktiven Interferenz der Ziel-Wellenlänge in der nullten Beugungsordnung führt;
• 48 in einer zu 47 ähnlichen Darstellung eine Variante der optischen Beugungskomponente nach 46, wobei ein Positiv-Beugungsstruktur-Niveau einerseits und ein Negativ-Beugungsstruktur-Niveau andererseits mit relativ zu einem Neutral-Beugungsstruktur-Niveau etwas zu großem Höhenunterschied ausgeführt sind, zur Veranschaulichung eines Beugungs-Kompensationseffektes, der sich bei einem solchen Höhenfehler ergibt;
• 49 in einer zu 46 ähnlichen Darstellung eine weitere Ausführung einer optischen Beugungskomponente mit drei Beugungsstruktur-Niveaus in einer im Vergleich zur Ausführung nach 46 anderen Abfolge;
• 50 eine weitere Ausführung einer optischen Beugungskomponente, wobei im Wesentlichen eine Gitterperiode dargestellt ist und wobei ein periodisches Gitter-Strukturprofil der optischen Beugungskomponente Beugungsstrukturen mit vier Beugungsstruktur-Niveaus aufweist; und
• 51 in einer zu 50 ähnlichen Darstellung eine weitere Ausführung einer optischen Beugungskomponente mit fünf Beugungsstruktur-Niveaus innerhalb einer Gitterperiode.

Embodiments of the invention are explained in more detail below with reference to the drawing. In this show:

• 1 schematically a projection exposure system for EUV microlithography;
• 2 Details of a light source of the projection exposure system in the vicinity of an EUV collector for guiding EUV useful light from a plasma source area to a field facet mirror of an illumination optics of the projection exposure system, the EUV collector being shown in a meridional section;
• 3 in a compared to the 3 a more abstract representation of a guidance on the one hand of EUV useful light and on the other hand of wavelength-different false light components with a reflection / diffraction at the EUV collector;
• 4th a plan view of a section of a grating surface of an optical grating with two diffraction gratings as diffraction structure groups with mutually perpendicular period running directions and the same grating periods, with three diffraction structure levels giving structure depths of in the 4th quadratic diffraction structures are illustrated via different hatching types, wherein the optical grating represents an embodiment of an optical diffraction component for suppressing at least one target wavelength by destructive interference;
• 5 in a diagram a wavelength-dependent reflectivity R of the optical grating 4th for a calculated ideal case and for a further, calculated, more realistic case and for a reference grating not according to the invention, the two diffraction gratings of the optical grating being designed to suppress two different wavelengths;
• 6th in one too 5 A similar diagram shows the relationships in an optical grating 4th , wherein the two diffraction gratings have identical structure depths, so that the optical grating is designed to suppress exactly one wavelength;
• 7th in one too 4th A similar representation shows a further embodiment of an optical grating with two diffraction gratings as diffraction structure groups with period running directions which assume an angle of 45 ° to one another, the optical grating representing an embodiment of an optical diffraction component for suppressing at least one target wavelength by destructive interference;
• 8th in one to the 4th and 7th A similar representation shows another embodiment of an optical grating with three diffraction gratings as diffraction structure groups, two of which have period running directions that are perpendicular to one another, and a third diffraction grating has a period running direction diagonal thereto, the optical grating being an embodiment of an optical diffraction component to suppress at least one target wavelength by destructive interference;
• 9 in one to the 5 and 6th similar diagram of reflection ratios in an optical grating 8th , in which all three diffraction gratings are designed to suppress one and the same wavelength;
• 10 in one too 9 Similar diagram the reflection ratios in an optical grating of the type 8th , the three diffraction gratings having different structure depths have so that the optical grating is designed to suppress different wavelengths;
• 11 in one too 8th A similar representation shows another embodiment of an optical grating with three diffraction gratings as diffraction structure groups with respective period running directions which in pairs assume an angle different from zero, the optical grating representing an embodiment of an optical diffraction component for suppressing at least one target wavelength by destructive interference ;
• 12 and 13th in one too 11 Similar representation of further designs of optical gratings, each with three diffraction gratings as diffraction structure groups with period running directions corresponding to those of the design according to 11 , the diffraction structures of the embodiments according to 12 and 13th to each other and in terms of execution according to 11 are arranged offset in the respective period running direction, the optical gratings representing further versions of optical diffraction components for suppressing at least one target wavelength by destructive interference;
• 14th a side view of a first diffraction structure group which belongs to a further embodiment of an optical diffraction component for suppressing at least one target wavelength through destructive interference, designed as a binary grating with a first grating period and a first structure depth;
• 15th in one too 14th A similar illustration shows another diffraction structure group as part of the optical diffraction component, the further diffraction structure group in turn being designed as a binary grating with a grating period and a structure depth, a possible overlay error in the production of this diffraction structure group is also indicated by dashed lines;
• 16 which appear as a superposition of the two diffraction structure groups after the 14th and 15th resulting diffractive optical component;
• 17th to 19th in to the 14th to 16 Similar representations of two diffraction structure groups as well as the further optical diffraction component resulting from this by superposition;
• 20th to 22nd in to the 14th to 16 Similar representations of two diffraction structure groups as well as the further optical diffraction component resulting from this by superposition;
• 23 in a diagram a reflectivity of an optical diffraction component of the type of that of 16 , 19th or 22nd wherein the structure height of the respective first diffraction structure group is fixed at a value for the suppression of a target wavelength and the reflectivity is plotted as a function of the structure height of the other diffraction structure group;
• 24 again in a diagram the reflectivity of the optical diffraction component, again with the structure depth of the first diffraction structure group fixed, plotted as a function of a difference in the structure depths of the two diffraction structure groups and normalized to the structure depth of the first diffraction structure group;
• 25th in one to 14th A similar representation of a diffraction structure group, designed as a binary grating with a grating period and a structure depth, as part of a further embodiment of an optical diffraction component for the suppression of at least one target wavelength by destructive interference, resulting from the superposition of three diffraction structure groups;
• 26th another diffraction structure group, again designed as a binary grating, to form this variant of the optical diffraction component;
• 27 another diffraction structure group, again designed as a binary grating, to form this variant of the optical diffraction component;
• 28 the optical diffraction component, formed as a superposition of the three diffraction structure groups after the 25th to 27 ;
• 29 to 32 in to the 25th to 28 Similar illustration of three diffraction structure groups, each again in the form of a binary grating with a grating period and a structure depth, as well as a further embodiment of an optical diffraction component resulting from this superposition to suppress at least one target wavelength through destructive interference.
• 33 in one to the 9 and 10 Similar diagram, wavelength-dependent reflection ratios for optical diffraction components like those according to one of the 8th , 11 to 13th , 28 or 32 , wherein the diffraction structure groups have different structure depths, so that the optical grating for suppressing different, compared to the variant according to 10 but is designed to be closer together at wavelengths;
• 34 in one too 4th Similar representation of a section of a grating surface of an optical grating with three diffraction gratings as diffraction structure groups, two of the gratings having parallel period running directions and a third grating having a period running direction perpendicular to it, and the diffraction structure groups with the same period running direction after Type of execution according to the 16 , 19th or 22nd overlay, with structure depths of in the 34 rectangular diffraction structures are illustrated via different hatch types, as a further embodiment of an optical diffraction component for suppressing at least one target wavelength by destructive interference;
• 35 a further embodiment of an optical diffraction component for suppressing at least one target wavelength by destructive interference, designed as a three-stage grating, designed for suppressing precisely one target wavelength, again in a schematic side view;
• 36 in one too 35 A similar illustration shows another embodiment of an optical diffraction component for suppressing at least one target wavelength through destructive interference, again designed with three diffraction structure levels that can be assigned to two diffraction structure groups, with variables that are used for the theoretical description of a calculation of a suppression efficiency the at least one target wavelength are shown;
• 37 in one to the 35 and 36 A similar illustration shows another embodiment of an optical diffraction component for suppressing at least one target wavelength by destructive interference, designed with four diffraction structure levels which can be assigned to a corresponding plurality of diffraction structure groups;
• 38 and 39 in to 37 Similar representations, two further designs of optical diffraction components for suppressing at least one target wavelength by destructive interference, again implemented with four diffraction structure levels;
• 40 in a diagram a wavelength-dependent reflectivity of an optical diffraction component with two diffraction structure groups according to the type, for example, of the embodiments according to 4th , 7th , 16 , 19th , 22nd , 35 , 36 , wherein the two diffraction structure groups are designed with structure depths for suppressing two DUV wavelengths;
• 41 in one too 40 In a similar illustration, a wavelength-dependent reflectivity for an optical diffraction component with a total of five diffraction structure levels, to which four diffraction structure groups with different structure depths can be assigned, two target wavelengths in the IR range above 10 µm and two target wavelengths in the DUV range being comparable to the target wavelengths 40 be suppressed;
• 42 an enlarged section 41 in the DUV range between 0.1 µm and 0.4 µm;
• 43 again in a diagram a wavelength-dependent reflectivity between 10.0 μm and 11.0 μm for different optical diffraction components with different slope tolerances of the diffraction structure groups;
• 44 the optical diffraction component according to 16 together with two lithographic mask structures which can be used in the production of the optical diffraction component for specifying boundary areas between adjacent surface sections of superimposed binary structures of the optical diffraction component;
• 45 in one too 44 the optical diffraction component according to a similar representation 19th together with two lithographic mask structures, which in turn can be used in the production of the optical diffraction component for specifying the boundary areas between the surface sections of the diffraction structure groups;
• 46 a further embodiment of an optical diffraction component for suppressing at least one target wavelength by destructive interference with a periodic grating structure profile with diffraction structures having three diffraction structure levels which are arranged in such a way that the target wavelength is suppressed by destructive interference;
• 47 the optical diffraction component according to 46 wherein the three diffraction structure levels have a height or level difference to one another, which leads to a perfect destructive interference of the target wavelength in the zeroth diffraction order;
• 48 in one too 47 a variant of the optical diffraction component according to a similar representation 46 , wherein a positive diffraction structure level on the one hand and a negative diffraction structure level on the other hand are designed with a height difference that is somewhat too great relative to a neutral diffraction structure level, to illustrate a diffraction compensation effect that results from such a height error;
• 49 in one too 46 A similar illustration shows a further embodiment of an optical diffraction component with three diffraction structure levels in one compared to the embodiment according to 46 other sequence;
• 50 a further embodiment of an optical diffraction component, wherein essentially a grating period is shown and wherein a periodic grating structure profile of the optical diffraction component has diffraction structures with four diffraction structure levels; and
• 51 in one too 50 Similar illustration shows another embodiment of an optical diffraction component with five diffraction structure levels within one grating period.

A projection exposure machine 1 for microlithography has a light source 2 for illuminating light or imaging light 3 , which is explained in more detail below. At the light source 2 it is an EUV light source that generates light in a wavelength range, for example between 5 nm and 30 nm, in particular between 5 nm and 15 nm. The illumination or imaging light 3 is also referred to below as EUV useful light.

At the light source 2 it can in particular be a light source with a wavelength of 13.5 nm or a light source with a wavelength of 6.9 nm. Other EUV wavelengths are also possible. A beam path of the illuminating light 3 is in the 1 shown extremely schematically.

For guiding the illuminating light 3 from the light source 2 towards an object field 4th in one object level 5 a lighting optic is used 6th . The latter includes one in the 1 Field facet mirror FF shown very schematically and one in the beam path of the illuminating light 3 subsequent pupil facet mirror PF, also shown in a highly schematic manner. Between the pupil facet mirror PF, which is in a pupil plane 6a the illumination optics is arranged, and the object field 4th is a field-forming mirror 6b for grazing incidence (GI mirror, grazing incidence mirror) in the beam path of the illuminating light 3 arranged. Such a Gl mirror 6b is not mandatory.

Pupil facets of the pupil facet mirror PF, which are not shown in detail, are part of a transmission optics, the field facets (also not shown) of the field facet mirror FF superimposing one another into the object field 4th transfer and especially depict. For the field facet mirror FF on the one hand and the pupil facet mirror PF on the other hand, an embodiment can be used which is known from the prior art. Such illumination optics are known, for example, from DE 10 2009 045 096 A1 .

With projection optics or imaging optics 7th becomes the object field 4th in an image field 8th in one image plane 9 shown with a given reduction scale. Projection optics that can be used for this are known, for example, from DE 10 2012 202 675 A1 .

To facilitate the description of the projection exposure system 1 as well as the different versions of the projection optics 7th a Cartesian xyz coordinate system is indicated in the drawing, from which the respective positional relationship of the components shown in the figures results. In the 1 the x-direction runs perpendicular to the plane of the drawing into it. The y-direction runs in the 1 to the left and the z direction in the 1 up. The object level 5 runs parallel to the xy plane.

The object field 4th and the field of view 8th are rectangular. Alternatively, it is also possible to use the object field 4th and field of view 8th bent or curved, that is to say in particular to be embodied in a partially annular shape. The object field 4th and the field of view 8th have an xy aspect ratio greater than 1. The object field 4th thus has a longer object field dimension in the x direction and a shorter object field dimension in the y direction. These object field dimensions run along the field coordinates x and y.

For the projection optics 7th one of the exemplary embodiments known from the prior art can be used. Here, a is mapped with the object field 4th coincident section of a reflection mask 10 also known as a reticle. The reticle 10 is held by a reticle holder 10a carried. The reticle holder 10a is driven by a reticle displacement drive 10b relocated.

The image through the projection optics 7th occurs on the surface of a substrate 11 in the form of a wafer held by a substrate holder 12 will be carried. The substrate holder 12 is driven by a wafer or substrate displacement drive 12a relocated.

In the 1 is schematic between the reticle 10 and the projection optics 7th a bundle of rays entering this 13th of the illumination light 3 and between the projection optics 7th and the substrate 11 one from the projection optics 7th outgoing beam 14th of the illumination light 3 shown. A numerical aperture (NA) on the image field side of the projection optics 7th is in the 1 not shown to scale.

The projection exposure system 1 is of the scanner type. Both the reticle 10 as well as the substrate 11 during operation of the projection exposure system 1 scanned in the y direction. Also a stepper type of projection exposure system 1 , in which between individual exposures of the substrate 11 a gradual displacement of the reticle 10 and the substrate 11 takes place in the y-direction is possible. These shifts take place in a synchronized manner with one another by appropriate control of the shift drives 10b and 12a .

2 shows details of the light source 2 .

At the light source 2 it is an LPP source (laser produced plasma). Tin droplets are used to generate plasma 15th from a tin droplet generator 16 generated as a continuous succession of droplets. A trajectory of the tin droplets 15th runs transversely to a main beam direction 17th of the EUV useful light 3 . The tin droplets 15th fly freely between the tin droplet generator 16 and a tin catcher 18th , being a plasma source area 19th step through. From the plasma source area 19th becomes the EUV useful light 3 emitted. In the plasma source area 19th the tin droplet arriving there becomes 15th with pump light 20th a pump light source 21st applied. At the pump light source 21st it can be an infrared laser source in the form of a CO ₂ laser, for example. Another IR laser source is also possible, in particular a solid-state laser, for example an Nd: YAG laser. The pump light source 21st may have a light source unit for generating a pre-light pulse and a light source unit for generating a main light pulse. The pre-light pulse on the one hand and the main light pulse on the other hand can have different light wavelengths.

The pump light 20th is about a mirror 22nd , which can be a regulated tiltable mirror, and a focusing lens 23 in the plasma source area 19th convicted. The application of pumped light results in the in the plasma source area 19th incoming tin droplets 15th on the EUV useful light 3 emitting plasma generated. A beam path of the EUV useful light 3 is in the 2 between the plasma source area 19th and the field facet mirror FF, as far as the EUV useful light from a collector mirror 24 is reflected, which is hereinafter also referred to as the EUV collector 24 is designated. The EUV collector 24 has a central opening 25th for that about the focusing lens 23 towards the plasma source area 19th focused pump light 20th . The collector 24 is designed as an ellipsoid mirror and transfers it from the plasma source area 19th , which is arranged in an ellipsoidal focal point, emitted useful EUV light 3 into an intermediate focus 26th of the EUV useful light 3 , the one in the other ellipsoid focal point of the collector 24 is arranged.

The field facet mirror FF is in the beam path of the EUV useful light 3 after the intermediate focus 26th in the area of a far field of the EUV useful light 3 arranged.

The EUV collector 24 and other components of the light source 2 , which is the tin droplet generator 16 , the tin catcher 18th and around the focusing lens 23 are in a vacuum housing 27 arranged. In the area of the intermediate focus 26th has the vacuum housing 27 a passage opening 28 . In the area where the pump light enters 20th into the vacuum housing 27 the latter has a pump light entry window 29 for the pre-light pulse and for the main light pulse.

3 shows, in a highly abstract manner, a guidance on the one hand from EUV useful light, i.e. the illuminating light 3 and on the other hand from false light 30th , in particular of longer-wave radiation, for example IR radiation with the wavelengths of the pre-light pulse and / or the main light pulse, between the plasma source area 19th the light source 2 and an intermediate focus plane 26a , in which the intermediate focus 26th is arranged. At the same time shows the 3 a variant of a lateral guidance of the pump light 20th towards the plasma source area 19th , so a guide in which there is a passage opening in the manner of the passage opening 25th in the EUV collector 24 not required. Both the useful light 3 as well as the false light 30th go from the plasma source area 19th out. Both the useful light 3 as well as the false light 30th meet surface sections 31 , 32 an entire impact area 33 of the EUV collector 24 . The surface sections 31 , 32 are sections of a grid surface of the EUV collector, also designated 33 in the drawing 24 , on which an optical Grid for diffractive removal of the false light radiation 30th is arranged. Designs for the optical grating are described below. The grid surface can only be at the location of the false light 30th acted upon surface sections 31 , 32 be arranged or, alternatively, larger sections of the impingement surface 33 cover and, in a further variant, the entire impact area 33 cover.

4th shows a portion of the grid surface 33 with an implementation of an optical grating 34 . The optical grating 34 represents an optical diffraction component for the suppression of at least one target wavelength by destructive interference.

The grating area of the optical grating 34 can be flat or curved, e.g. B. concave like the impact surface 33 at the collector mirror 24 after the 2 and 3 , or convex.

The optical grating 34 has as diffraction structure groups with two on the grating surface 33 arranged diffraction gratings 35 , 36 . The diffraction grating 35 is also referred to below as the first diffraction grating. The diffraction grating 36 is also referred to below as the second diffraction grating.

At the diffraction grating 35 diffraction positive structures run 37 and diffraction negative structures 38 alternating in each case 4th horizontal. One period running direction 39 this first diffraction grating 35 runs vertically. For this horizontal course of the diffraction structures 37 , 38 , the period runs 39 in the 4th so vertically.

The second diffraction grating 36 has in the 4th vertical diffraction positive structures 40 and thereby alternating negative diffraction structures 41 . One period running direction 42 of the second diffraction grating 36 runs in the 4th again perpendicular to the diffraction structures 40 , 41 , so horizontally.

The diffraction structures 37 , 38 or. 40 , 41 of the two diffraction gratings 35 , 36 of the optical grating 34 are realized by four diffraction structure types or diffraction structure levels, which differ in their structure depth and in the 4th through different hatching types and through numbers applied to the respective diffraction structure 1 , 2 , 3 , 4th illustrated. The diffraction structure type " 1 "Has the structure depth 0. The diffraction structure type" 2 "Has the structure depth" dv ". The type of diffraction structure " 2 “Occupied area of the grid area is perpendicular to the plane of the drawing 4th by the structure depth dv deeper than the diffraction structure type " 1 ".

The respective structure depth can be assigned a depth value relative to a reference plane, the reference plane generally selected as the one in which no material is removed (structure depth = 0).

The respective areas of the diffraction structure types " 1 "To" 4 "are each square. Other boundary forms of the diffraction structure types are also possible, which result in a complete coverage of the grating surface.

The diffraction structure type " 3 "Has a, again relative to the diffraction structure type" 1 “Perpendicular to the plane of the drawing 4th measured, structure depth ie. The diffraction structure type "4" has a correspondingly measured structure depth dv + dh.

The four diffraction structure types " 1 "To" 4 "are for the optical grating 34 each arranged in a 2 × 2 array, the diffraction structure type " 1 "Top left, the diffraction structure type" 2 "Top right, the diffraction structure type" 3 "Bottom left and the diffraction structure type" 4th “Is arranged at the bottom right. These 2 × 2 arrays of such groups, each of the 4 diffraction structure types, are again after the execution 4th arranged in a superstructure in the form of a 3 × 3 array. Generally speaking, the optical grating 34 on the grid surface 33 Of course, horizontally and vertically as required by adding further corresponding 2 × 2 arrays of the four diffraction structure types " 1 " to " 4th " expand.

In the direction of the period 39 of the first diffraction grating 35 thus follow one another with positive diffraction structures 37 and in comparison to the structure depth, ie deeper-lying diffraction negative structures 38 . In the direction of the period 42 follows at the second diffraction grating 36 each on one of the positive diffraction structures 40 a negative diffraction structure lying deeper by the structure depth dv 41 . In the optical Grid 34 are therefore two superimposed diffraction gratings 35 , 36 realized with respective structure depths dh and dv.

When running after 4th the structure depth is the difference in height between the respective diffraction positive structures and the associated diffraction negative structures. More generally, the structure depth can be understood as the optical path difference between the diffraction positive structures and the associated diffraction negative structures.

On the diffraction positive structures 37 , 40 and the diffraction negative structures 38 , 41 can apply a highly reflective coating to the optical grating 34 be applied and possibly an auxiliary layer.

The auxiliary layer which is arranged below the highly reflective coating can be a layer that has a service life of the optical grating 34 elevated. Alternatively or additionally, an auxiliary layer can also be applied to the highly reflective coating in order to protect it from damage.

The highly reflective coating can be a multilayer layer, as is known for the highly effective reflection of, in particular, radiation with EUV wavelengths.

The diffraction grating 35 , 36 of the optical grating 34 are each designed as a binary grid. The area of the positive diffraction structures is equal to the area of the negative diffraction structures.

One grating period of the diffraction grating 35 can be in the range between 0.5 mm and 5 mm and, for example, 2 mm. One grating period of the diffraction grating 36 can be in the range between 0.5 mm and 5 mm and, for example, 2 mm. Such a grating period is in FIG 4th for the second diffraction grating 36 denoted by P. A structure flank of the respective diffraction structures 37 , 38 , 40 , 41 can be perpendicular to the extent of the respective diffraction structure, i.e. measured in the respective period running direction 39 or. 42 , have a dimension in the range between 1 µm and 10 µm and for example in the range of 5 µm. Such a flank extension or flank extension is for the second diffraction grating 36 in the 4th strongly exaggerated large indicated at F.

5 shows in a diagram the result of a calculation of a wavelength-dependent reflectivity of the optical grating 34 for the design parameters dv = 2.65 µm and dh = 2.55 µm. At 43 is a reflectivity of the optical grating 34 plotted, which results as the result of a calculation in which it is also assumed that the flank extension F is 0, i.e. the result for an optical grating 34 with ideally steep flanks between the diffraction structures. In the case of the suppression design wavelengths of 10.2 μm and 10.6 μm for corresponding stray light wavelengths, which are also referred to as target wavelengths, there is a suppression of reflectivity of the optical grating 34 ideally the reflectivity curve 43 of better than 10 ^-8 . These two wavelengths correspond to the wavelengths of the prepulse and the main pulse of the pump light source 21st .

The following applies to the two target wavelengths 10.2 µm (λ ₁ ) and 10.6 µm (λ ₂ ): $${\left({\mathrm{\lambda }}_1-{\mathrm{\lambda }}_2\right)}^2/{\left({\mathrm{<figure-callout\; id="1"\; label="\lambda "\; filenames="DE102019210450A1\_0015.png,DE102019210450A1\_0026.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_1\mathrm{+}{\mathrm{\lambda }}_2\right)}^2=3.77\cdot {10}^{-\mathrm{4th}}$$

For this normalized target wavelength ratio, the following applies: $${\left({\mathrm{\lambda }}_1-{\mathrm{\lambda }}_2\right)}^2/{\left({\mathrm{<figure-callout\; id="1"\; label="\lambda "\; filenames="DE102019210450A1\_0015.png,DE102019210450A1\_0026.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_1\mathrm{+}{\mathrm{\lambda }}_2\right)}^2<10\%$$

At 44 is in the 5 a reflectivity curve R (λ) is plotted, in which certain tolerances are taken into account with regard to the accuracy of the generation of the structure depths dv and that on the one hand as well as the slope. At the target wavelengths of 10.2 µm and 10.6 µm, the reflectivity suppression is better than 10 ^-6 .

For comparison, the 5 another reference reflectivity curve 45 entered that the suppression result for an optical reference grating with exactly one diffraction grating, so z. B. either the diffraction grating 35 with the horizontal diffraction structures or with the diffraction grating 36 with the vertical diffraction structures is realized. The same tolerances are taken into account for the generation of the structure depth and the slope as for the reflectivity curve 44 . It can be seen that, despite the same tolerances, the reference reflectivity curve 45 has a significantly lower optimal reflectivity suppression in the range of 10 ^-4 . As the reference grid to which the reference reflectivity curve 45 was calculated, and also has only one diffraction grating, only exactly one wavelength is suppressed here, namely 10.6 µm.

The two diffraction gratings 35 , 36 have a ratio between a grating period (2 mm) and a structure depth (in the range of 2.6 µm) which is significantly greater than 10 and actually greater than 500 and in the range of 1000.

Because of the design of the two diffraction gratings 35 , 36 the binary grating is an area ratio of the areas of the diffraction positive structures 37 , 40 to surfaces of the diffraction negative structures 38 , 41 at 1. Depending on the design of the optical grating 34 this area ratio can also deviate from 1 and can be in the range between 0.9 and 1.1.

The two diffraction gratings 35 , 36 have the same grating period P, so that a period ratio of the two grating periods is 1. Depending on the design of the optical grating 34 the period ratio can be in the range between 0.9 and 1.1. The differences between the two grating periods can also be significantly greater, so that, for example, a period ratio of 1: 2 or 1: 5 results.

6th shows a variant of the optical grating 34 , in which the structure depths dv, ie are the same size and have an amount of 2.65 µm. Both diffraction gratings 35 , 36 then contribute to the suppression of the false light wavelength 10.6 µm. Correspondingly, even better suppression ratios result with the ideal reflectivity curve 43 and the reflectivity curve calculated with the design tolerances 44 .

7th shows in one too 4th Similar illustration of a variant of the optical grating that replaces the optical grating 34 after 4th can be used as an optical diffraction component to suppress at least one target wavelength due to destructive interference. Components and functions corresponding to those described above with reference to the 4th have already been explained have the same reference numerals and will not be discussed again in detail.

The optical grating 46 after 7th differs from that of the 4th mainly by having a period running direction 39 of the first diffraction grating 35 does not run vertically, but at an angle of 45 ° to the horizontal. The diffraction structure types result accordingly " 1 " to " 4th “With diamond-shaped surfaces.

8th Figure 3 shows another embodiment of an optical grating 47 , which can be used as an alternative or in addition to the optical gratings described above as an optical diffraction component for suppressing at least one target wavelength through destructive interference. Components and functions corresponding to those described above with reference to the 1 to 7th and particularly with reference to the 4th to 7th have already been explained, have the same reference numerals and are not discussed again in detail.

The optical grating 47 has a total of three diffraction gratings as diffraction structure groups, two of these three diffraction gratings being the diffraction gratings 35 and 36 according to the execution 4th correspond. One grating period of the diffraction grating 35 is in the 8th illustrated at ph and a grating period of the diffraction grating 36 at pv.

A third diffraction grating 48 of the optical grating 47 has diagonal to the diffraction structures 37 , 38 such as 40 , 41 of the first two diffraction gratings 35 , 36 positive diffraction structures 49 and diffraction negative structures 50 . Compared to the diffraction positive structures 49 have the diffraction negative structures 50 a structure depth that is in the 8th is illustrated with dd.

An entire height profile over the entire illustrated section of the grating surface of the optical grating 47 can be understood as a series of base sections in the form of 2 × 4 arrays, which are specified by the boundaries of the horizontally extending diffraction structures 37 , 38 of the diffraction grating 35 and the vertically extending diffraction structures 40 , 41 of the diffraction grating 36 . Diffraction structure types or diffraction structure levels on this 2 × 4 array are on the top left in FIG 8th arranged 2 × 4 array labeled "000", "001", "010", "011", "100", "101", "110" and "111".

The following table gives the structure depths of these diffraction structure types and their area proportions in units of the grating periods ph, pv: Table 1 Diffraction structure type Structure depth Area share 000 0 (ph + pv) / 4 001 dd (ph + pv) / 4 010 dv (ph + pv) / 4 011 dv + dd (ph + pv) / 4 100 ie (ph + pv) / 4 101 dh + dd (ph + pv) / 4 110 dh + dv (ph + pv) / 4 111 dh + dv + dd (ph + pv) / 4

All diffraction structure types “000” to “111” have the same area ratio (ph + pv) / 4 in the total area of the optical grating 47 . This ensures that all three diffraction gratings 35 , 36 and 48 of the optical grating 47 Represent binary grating and their positive diffraction structures 37 , 40 , 49 each to their negative diffraction structures 38 , 41 , 50 have an area ratio of 1.

One period running direction 51 of the third diffraction grating 48 runs along a grating period pd at an angle of approximately 23 ° to the direction of the period 39 of the diffraction grating 35 . This period running direction 51 is together with an offset of an arrangement of the diffraction structures 49 , 50 of the third diffraction grating 48 chosen so that boundaries between the diffraction structures 49 , 50 of the third diffraction grating 48 run along the diagonals of two horizontally adjacent structural fields, which are formed by the intersecting diffraction structures 37 , 38 on the one hand and 40 , 41 on the other hand. An offset variation of this arrangement of the diffraction structures 49 , 50 along the period running direction 51 of the third diffraction grating 48 is possible, as in the 8th by a double arrow 52 indicated.

The grating period pd of the third diffraction grating 48 is in the order of magnitude of the grating periods ph, pv and is in the case of the optical grating 47 about 1.7mm.

9 shows in one to the 5 and 6th Similar representation, data on the wavelength-dependent reflectivity R for the case that the structure depths dh, dv and dd are each the same size and in the example described have the value 2.65 μm.

At 53 is in the 9 a reflectivity for the ideal case of perfectly steep flanks (flank extension 0) for the diffraction grating 35 , 36 and 48 shown. A reflectivity suppression of a target wavelength of 10.6 µm is orders of magnitude better than 10 ^-10 .

At 54 the calculated result of the wavelength-dependent reflectivity is shown for the structure depths of the diffraction structures 37 , 38 , 40 , 41 , 49 , 50 and realistic tolerances would be assumed for the flank extensions. It results for the optical grating 47 with the three diffraction gratings 35 , 36 , 48 a reflectivity suppression that is less than the ideal case, but is still significantly better than 10 ^-10 .

As reference values in the 9 nor the reflectivity curves 44 and 45 according to the 6th for the optical grating 34 with the two diffraction gratings 35 , 36 on the one hand and for the conventional optical grating with exactly one diffraction grating.

• dh = 2,55 µm, dv = 2,65 µm und dd = 0,26 µm.

10 again shows the reflectivity ratios of an embodiment of the optical grating in a wavelength-dependent diagram 47 with the following structure depths:

• dh = 2.55 µm, dv = 2.65 µm and dd = 0.26 µm.

The structure depth dd of the diagonal diffraction structures 49 , 50 is therefore by about a factor 10 less than the structure depths of the diffraction structures 37 , 38 , 40 , 41 the diffraction grating 35 , 36 of the optical grating 47 .

At 55 is in the 10 the reflectivity in turn for an ideal design of such an optical grating 47 shown with flank extension 0. For the two suppression wavelengths at around 10.2 µm (λ ₁ ) and around 10.59 µm (λ ₂ ) and at a further wavelength in the range of 1.05 µm, a reflectivity suppression of the optical grating is in the range of 10 ^-8 or better.

For the two IR wavelengths λ ₁ , λ ₂ , those with the optical grating 47 are suppressed as target wavelengths, what applies above in connection with the optical grating again applies to the normalized difference between the target wavelengths 34 after 4th was explained.

At 56 is in the 10 in turn, a reflectivity curve with predetermined tolerances is calculated for the structure depths on the one hand and the flank extension on the other.

Based on 11 is another embodiment of an optical grating below 57 , again with three diffraction gratings 35 , 36 , 48 described. Components and functions corresponding to those described above with reference to the 1 to 10 and in particular with reference to the 8th have already been explained, have the same reference numerals and are not discussed again in detail.

The optical grating 57 differs from the optical grating 47 mainly in the orientation of the three cycle directions 39 , 42 and 51 of the three superimposed diffraction gratings 35 , 36 and 48 . The period running direction 39 of the first diffraction grating 35 runs at an angle of about 23 ° to the vertical in the 11 . The period running direction 42 of the second diffraction grating 36 runs horizontally.

The period running direction 51 of the third diffraction grating 48 runs again at an angle of about 23 ° to the vertical, with the two periods running directions 39 and 51 of the first diffraction grating 35 on the one hand and the third diffraction grating 48 on the other hand, assume an angle of about 46 ° to each other.

In the 11 is a diamond-shaped base portion of the optical grating 57 corresponding to the 2 × 4 array of the optical grating 47 again highlighted with diffraction structure types “000” to “111”. An assignment of the structure depths and also the area proportions is for these diffraction structure types “000” to “111” of the optical grating 57 exactly as in Table 1 above 8th specified.

An offset of structure boundaries of the third diffraction grating 48 along the period running direction 51 is at the optical grating 57 so that there are structural boundaries between the diffraction structures 37 , 38 of the first diffraction grating 35 , between the diffraction structures 40 , 41 of the second diffraction grating 36 and between the diffraction structures 49 , 50 of the third diffraction grating 48 each at a point P in the center of the 11 cut the base section shown.

With the optical grating 57 the grating period ph is about 3.25 mm, the grating period pv is 2 mm and the grating period pd is exactly as large as the grating period ph.

12 and 13th show further designs of optical gratings 58 , 59 moving away from the optical grating 57 only in the size of the offset of the arrangement of the structure boundaries between the diffraction structures 49 , 50 along the period running direction 51 distinguish. With the optical grating 58 after 12 this offset is such that the structure boundaries of the different diffraction gratings 35 , 36 , 48 do not cut at one point in the respective base section. With the optical grating 59 after 13th the offset is such that the structure boundaries of the three diffraction gratings 35 , 36 , 48 compared to execution after 11 cut at other positions within the respective base section, so that in turn a different distribution of the diffraction structure types "000" to "111" results.

The assignment of the structure depths and the area proportions of the 12 and 13th Diffraction structure types “000” to “111” indicated within the highlighted unit cells are again as shown in Table 1 for 8th specified.

Based on 14th to 16 is another embodiment of an optical grating below 60 explained as an optical diffraction component for the suppression of at least one target wavelength by destructive interference. Components and functions that correspond to those mentioned under Reference to the 1 to 13th have already been explained, have the same reference numerals and are not discussed again in detail.

The optical grating 60 is as a superposition of two diffraction gratings 61 , 62 executed individually in 14th (Diffraction grating 61 ) and 15th (Diffraction grating 62 ) are shown. The diffraction grating 61 , 62 represent diffraction structure groups for the suppression of a respective target wavelength.

The diffraction grating 61 has a structure depth d ₁ and a grating period p ₁ . The diffraction grating 62 has a structure depth d ₂ and a grating period p ₂ . The two diffraction gratings 61 , 62 are each designed as a binary grid.

This by superimposing the two diffraction gratings 61 , 62 resulting optical grating 60 has a total of three diffraction structure levels or diffraction structure types with structure depths of 0 (diffraction structure level N ₁ ), Structure depth d ₂ (diffraction structure level N ₂ ), with structure depth d ₁ (diffraction structure level N ₃ ) and with structure depth d ₁ + d ₂ (diffraction structure level N ₄ ).

The grating periods p ₁ and p ₂ are in the optical grating 60 equal. The structure depths d ₁ , d ₂ are for the optical grating 60 different. With respect to a common period running direction x of the diffraction gratings 61 and 62 are these two diffraction gratings 61 and 62 to each other about a quarter of the common period, in other words p _1/4 = p _2/4 phase with each other.

The dashed line is in the 15th and 16 an overlay bug 63 illustrated along the period running direction x. One such overlay bug 63 can be seen as a phase error of the superposition of the two diffraction gratings 61 , 62 can be understood along the period running direction and leads to a change in the extent of the various diffraction structure levels N ₁ , N ₂ , N ₃ , N ₄ along the period running direction x.

In the event that the two structure depths d ₁ and d ₂ in an alternative embodiment of the optical grating 60 are equal, the two diffraction structure levels degenerate N ₂ , N ₃ to a common structure level, so that such an optical grating, consisting of two diffraction gratings with the same structure depths, has exactly three diffraction structure levels.

Based on 17th to 19th is another embodiment of an optical grating below 60 explained as an optical diffraction component for the suppression of at least one target wavelength by destructive interference. Components and functions corresponding to those described above with reference to the 1 to 16 and in particular with reference to the 14th to 16 have already been explained, have the same reference numerals and are not discussed again in detail.

19th shows an optical grating 64 , which is a superposition of two diffraction structure groups in the form of diffraction gratings 65 ( 17th ) and 66 ( 18th ) results.

• p₁= p₂ und d₁ = d₂.

With the diffraction gratings 65 , 66 applies:

• p ₁ = p ₂ and d ₁ = d ₂ .

A phase shift of the two diffraction gratings 65 , 66 each other along the running direction of period x is p _1/4 = p _2/4.

A ratio of extension between positive diffraction structures 67 , 68 the diffraction grating 65 , 66 on the one hand and the associated negative diffraction structures 69 , 70 on the other hand is exactly inverted to each other, so that the diffraction positive structures 67 have the same extent along the period running direction x as the diffraction negative structures 70 of the diffraction grating 66 and the diffraction negative structures 69 of the diffraction grating 65 have the same extension along the period running direction x as the diffraction positive structures 68 of the diffraction grating 66 . The extensions of the positive diffraction structures 67 , 68 on the one hand and the negative diffraction structures 69 , 70 on the other hand are at the respective diffraction grating 65 , 66 so not the same, so that in this sense the two diffraction gratings 65 , 66 are not binary grids. The aspect ratio can deviate very clearly from 1: 1 and is the same for the diffraction gratings 65 , 66 about 1: 3. Also another aspect ratio between the diffraction positive structures 67 , 68 on the one hand and the diffraction negative structures 69 , 70 on the other hand of the respective diffraction grating 65 , 66 in the range between 10: 1 and 1:10 is possible.

In the 18th and 19th is again an overlay bug 63 indicated. Unlike the optical grating 60 the overlay error results 63 with the optical grating 64 does not result in a change in the area ratios between the three diffraction structure levels N ₁ (Structure depth 0), N ₂ (Structure depth d ₁ = d ₂ ) and N ₃ (Structure depth d ₁ + d ₂ ) along the period running direction x.

Based on 20th to 22nd is another embodiment of an optical grating below 60 explained as an optical diffraction component for the suppression of at least one target wavelength by destructive interference. Components and functions corresponding to those described above with reference to the 1 to 19th and particularly with reference to the 14th to 19th have already been explained, have the same reference numerals and are not discussed again in detail.

22nd shows an optical grating 71 , that as a superposition of two diffraction gratings 72 ( 20th ) and 73 ( 21st ) results.

The diffraction grating 72 has a structure depth d ₁ and a grating period p ₁ . The diffraction grating 73 has a structure depth d ₂ and a grating period p ₂ = 2p ₁ . The following applies: d ₁ ≠ d ₂ .

Both diffraction gratings 72 , 73 are designed as binary grids with the same extent of the diffraction positive structures and the diffraction negative structures along the period running direction x.

The optical grating 71 has four diffraction structure levels, viz N ₁ (Structure depth 0), N ₂ (Structure depth d ₂ ), N ₃ (Structure depth d ₁ ) and N ₄ (Structure depth d ₁ + d ₂ ).

In the 21st and 22nd again, dashed lines represent an overlay error 63 due to a phase shift of the two diffraction gratings 72 , 73 shown along the period running direction x. Due to the dimensional proportions of the two diffraction gratings 72 , 73 the overlay errors are canceled out 63 what the relative extensions of the diffraction structure levels N and N ₂ is concerned, straight out, so that, each over a period p _{2 of} the optical grating 71 seen the ratio of extents of the diffraction structure levels N ₁ and N ₂ regardless of the size of the overlay error 63 does not change.

Due to the dimensional proportions of the two diffraction gratings 72 , 73 there are level changes caused by the diffraction grating 73 be brought about, each with a diffraction structure type of the diffraction grating 72 , in this case with its diffraction positive structures. The phase relationship between the two diffraction gratings 72 , 73 along the period direction x is such that flanks F of the diffraction grating 72 , 73 do not overlay at the same place along the period running direction x.

23 FIG. 13 shows an optical grating of the type described above with reference to FIG 14th to 22nd described optical grating 60 , 64 or 71 the dependence of a reflectivity R of the optical grating, the first diffraction grating in each case with structure depth d _{1 being} designed for the suppression of a target wavelength of 10.6 microns through destructive interference, on the structure depth d _{2 of} the respective second diffraction grating from which this optical Grid is built. For a structure depth d ₂ of 2.65 µm, that is to say at about a quarter of the target wavelength, the maximum suppression of the target wavelength results (reflectivity less than 10 ^-8 ).

Tolerances of the structure depths or the slope are included in the associated reflectivity curve 74 considered.

The closer the second structure depth d ₂ comes to the recorded first structure depth d ₁ of 2.65 μm, the better the suppression of the target wavelength. An improvement in the suppression effect achieved by the first diffraction grating with structure depth d ₁ is already in the area of structure depth d ₂ between 0 and approximately twice the structure depth d ₁ , i.e. in the 23 in the range between about 0.2 µm and 5 µm. For the design of the two structure depths d ₁ and d _{2, the} result is that from a certain proximity of the two structure depths to each other, the suppression effect of the two diffraction gratings with the structure depths d ₁ and d ₂ mutually reinforces. The following relationship was found as a condition for a distance between the two target wavelengths λ ₁ (for the first diffraction grating) and λ ₂ (for the second diffraction grating) so that a suppression effect mutually reinforces: $$\left|{\mathrm{\lambda }}_2-{\mathrm{<figure-callout\; id="1"\; label="\lambda "\; filenames="DE102019210450A1\_0015.png,DE102019210450A1\_0026.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_1\right|/{\mathrm{<figure-callout\; id="1"\; label="\lambda "\; filenames="DE102019210450A1\_0015.png,DE102019210450A1\_0026.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_1<0.5$$

Assuming that the two target wavelengths are not too different from each other, this condition can be written as follows, regardless of whether it is related to the first wavelength λ ₁ or the second wavelength λ ₂ and without an absolute value: $${\left({\mathrm{\lambda }}_1-{\mathrm{\lambda }}_2\right)}^2/{\left({\mathrm{<figure-callout\; id="1"\; label="\lambda "\; filenames="DE102019210450A1\_0015.png,DE102019210450A1\_0026.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_1\mathrm{+}{\mathrm{\lambda }}_2\right)}^2<0.1$$

Insofar as these conditions are met for the two target wavelengths λ ₁ , λ ₂ that are to be suppressed with the two diffraction gratings, i.e. the two diffraction structure groups of the optical diffraction component, the suppression increases at the two target wavelengths λ ₁ , λ ₂ each other.

This is in the 24 plotted as the dependence of the reflectivity on the structure depth difference (d ₂ - d ₁ ) / (d ₁ ) normalized to the first structure depth in the value range between -1.0 and 1.0. The corresponding reflectivity curve 75 is between the values -0.5 and 0.5 for this normalized structure depth difference already clearly below an asymptotic reflectivity value for larger structure depth differences.

Based on 25th to 28 is another embodiment of an optical grating below 60 explained as an optical diffraction component for the suppression of at least one target wavelength by destructive interference. Components and functions corresponding to those described above with reference to the 1 to 24 and in particular with reference to the 14th to 22nd have already been explained, have the same reference numerals and are not discussed again in detail.

• d₁ > d₂ > d₃.

28 shows an optical grating 76 , which as a superposition of three diffraction gratings 77 ( 25th ), 78 ( 26th ) and 79 ( 27 ) results. For the structure depths d ₁ , d ₂ , d _{3 of} these three diffraction gratings 77 to 79 applies:

• d ₁ > d ₂ > d ₃ .

The three diffraction gratings 77 to 79 are each designed as a binary grid.

• p₁: p₂: p₃ = 1 : 2 : 4.

For the ratio of the grating periods p ₁ , p ₂ and p _{3 of} the three diffraction gratings 77 to 79 applies:

• p ₁ : p ₂ : p ₃ = 1: 2: 4.

The result is an optical diffraction component with which basically three different target wavelengths can be suppressed by destructive interference and that with the three diffraction gratings 77 to 79 has three diffraction structural groups. The optical grating is based on this period ratio 76 not sensitive to an overlay error, i.e. in relation to a possible phase offset of the diffraction structures of the three diffraction gratings 77 to 79 along the period running direction x.

The optical grating 76 has the following eight diffraction structure levels: N ₁ (Structure depth 0), N ₂ (Structure depth d ₃ ), N ₃ (Structure depth d ₂ ), N ₄ (Structure depth d ₁ ), N ₅ (Structure depth d ₂ + d ₃ ), N ₅ (Structure depth d ₃ + d ₁ ), N ₇ (structure depth d ₁ + d ₂ ) and N ₈ (Structure depth d ₁ + d ₂ + d ₃ ). These diffraction structure levels can correspond to the three diffraction structure groups of the three diffraction gratings 77 to 79 be assigned.

Based on 29 to 32 is another embodiment of an optical grating below 60 explained as an optical diffraction component for the suppression of at least one target wavelength by destructive interference. Components and functions corresponding to those described above with reference to the 1 to 28 and in particular with reference to the 25th to 28 have already been explained, have the same reference numerals and are not discussed again in detail.

• p₁: p₂: p₃= 2 : 2 : 1.

32 shows an optical grating 80 , which is achieved by superimposing three binary diffraction gratings 81 ( 29 ), 82 ( 30th ) and 83 ( 31 ) results. For the structure depths d ₁ , d ₂ , d _{3 of} the three diffraction gratings 81 to 83 it holds that d ₁ > d ₂ > d ₃ . For the grating periods p ₁ , p ₂ and p ₃ the diffraction grating 81 to 83 applies:

• p ₁ : p ₂ : p ₃ = 2: 2: 1.

An overlay error of a phase relationship between the diffraction structures of the three diffraction gratings 81 to 83 along the period running direction x plays according to what has been said above about the explanations after 14th to 22nd and 25th to 28 was explained, only in relation to the relationship between the diffraction gratings 81 and 82 matter because they have the same grating period.

Also the optical grating 80 has eight different diffraction structure levels corresponding to the three diffraction structure groups of the three diffraction gratings 81 to 83 can be assigned.

33 shows in one example to the 5 and 10 Similar representation, the suppression effect of an optical grating on the type of embodiments according to the 28 and 32 , having three diffraction structure groups for the suppression of three different target wavelengths.

A reflectivity curve 84 shows the wavelength-dependent suppression for the structure depths d ₁ = 2.65 µm, d ₂ = 2.55 µm and d ₃ = 2.60 µm, i.e. designed to suppress the target wavelengths 10.2 µm, 10.40 µm and 10 , 6 µm, with a flank extension F of 0 along the period running direction x, ie an ideally steep course of the diffraction structures of the associated diffraction grating. The three target wavelengths result in a suppression better than 10 ^-11 .

At 85 is in the 33 A reflectivity curve is plotted, which in turn takes into account structure depth and edge steepness tolerances. For the target wavelengths at the edge, 10.2 µm and 10.6 µm, the reflectivity curve results 85 a suppression of better than 10 ^-9 and at the central target wavelength 10.40 µm a suppression in the range of 10 ^-10 .

As references are in the 33 the reflectivity curves 44 and 45 for an optical grating with exactly two diffraction gratings and for an optical grating with exactly one diffraction grating (see also 5 ).

34 Figure 3 shows another embodiment of an optical grating 86 as an optical diffraction component to suppress at least one target wavelength through destructive interference. Components and functions corresponding to those described above with reference to the 1 to 33 and in particular with reference to the 4th to 8th have already been explained, have the same reference numerals and are not discussed again in detail.

The optical grating 86 results as a superposition of a total of three diffraction gratings 87 , 88 , 89 . Two of these diffraction gratings, namely the diffraction gratings 87 and 88 have a period running direction x, which is in the 34 runs horizontally. The third diffraction grating 89 has a period running direction y, which is in the 34 runs vertically. Similar to the 4th and 7th are at the optical grating 86 Diffraction structure types, i.e. different diffraction structure levels highlighted with different hatching. If the three diffraction gratings arise 87 to 89 have three different structure depths d ₁ , d ₂ and d ₃ , again eight different diffraction structure levels, which correspond to the eight different hatch types. If two of the three structure depths d ₁ , d ₂ and d _{3 of} the diffraction grating 87 to 89 or all three structure depths are the same, there is a correspondingly smaller number of different diffraction structure levels.

In the embodiment according to the optical grating 86 is a suppression of the respective target wavelength independent of overlay errors.

As far as the number of diffraction structure levels is concerned, reference is made to the explanations given above regarding the designs of the optical gratings 76 after 28 and 80 after 32 .

Using the example of one in the 35 shown optical diffraction component 91 with three diffraction structure levels, basic properties of such diffraction components are explained below. Components and functions corresponding to those described above with reference to the 1 to 34 have already been explained, have the same reference numerals and are not discussed again in detail. The diffraction structure levels are in 35 With N ₁ , N ₂ and N ₃ designated.

The target wavelength to be suppressed has a wavelength of λ _N.

The diffraction structure level N ₁ has a structure depth of 0. The diffraction structure level N ₂ has a structure depth d of λ _N / 6. The deepest diffraction structure level N ₃ has a structure depth of 2d (= λ _N / 3).

A superposition of a total of n diffraction gratings with structure depths d ₁ , d ₂ , ... d _n is suitable for suppressing a total of n target wavelengths λ ₁ , λ ₂ , ... λ _n . The number of possible diffraction structure levels is 2 ⁿ . With three structure depths d ₁ , d ₂ , d ₃ , as explained above, eight diffraction structure levels result N ₁ to N ₈ . The different diffraction structure levels N _i are preferred arranged that all diffraction structure levels N _i equal area proportions of the total area of the diffraction component 91 take in.

The diffractive optical component 91 represents as a variant a so-called m-stage grating with three stages in this case. Such an m-stage grating consists of m different diffraction structure levels, each of which occupies the same area and structure height differences of d = λ _N / (2m) have to each other. Here, with lower wavelength sensitivity, good suppression of the target wavelength λ _N results.

Following the three-step grid 35 a grating period P is assigned, after which the sequence of the three diffraction structure levels N ₁ , N ₂ , N ₃ identical repeated.

36 Figure 3 shows another embodiment of a diffractive optical component 92 to suppress at least one target wavelength through destructive interference. The diffraction structure levels Ni in the area around a lowest lying diffraction structure level are shown N _n , namely the diffraction structure levels N _n-2 , N _n-1 , N _n , N _{n + 1} , N _{n + 2} .

1(0) ist dabei die Intensität in der nullten Beugungsordnung, also das Betragsquadrat der Feldamplitude des gebeugten Fernfeldes.An intensity of reflected light in the zeroth diffraction order can, based on the Fraunhofer approximation for the diffracted far field, be written in simplified form for an N-stage, periodic phase grating as follows: $$\text{I.}\left(0\right)={\left|\text{E.}\left(0\right)\right|}^2={\left|{\displaystyle {\sum }_{n=0}^{N-1}{\mathrm{L.}}_n{e}^{-i\mathrm{4th}\pi \frac{H_n}{\lambda }}}\right|}^2$$

1 (0) is the intensity in the zeroth diffraction order, i.e. the square of the magnitude of the field amplitude of the diffracted far field.

N is the number of stages of the phase grating. L _n is a phase term assigned to the respective grid level. This phase term L _n , which corresponds to the extension of the respective diffraction structure level N _i along the period running direction x, is in FIG 36 illustrated. h _n is a measure of the structure depth of the respective diffraction structure level (cf. 36 ). λ is the wavelength of the diffracted light.

Based on 37 is another embodiment of a diffractive optical component 93 for the suppression of at least one target wavelength by destructive interference. Components and functions corresponding to those described above with reference to the 1 to 36 and in particular with reference to the 36 have already been explained, have the same reference numerals and are not explained again in detail.

37 shows a further embodiment of a stair lattice with the same structure depths of the various lattice steps, here designated as h ₀ , and the same lengths of the diffraction structure levels N ₁ , N ₂ , N ₃ and N ₄ along the running direction of the period, in this case denoted by R. The period running direction R can also be the radius of a concentric diffraction structure, with a center of this diffraction structure then with a center of the collector mirror 24 can coincide.

The diffraction component 93 thus has a total of four diffraction structure levels N ₁ to N ₄ whose structure depths differ by h ₀ . The following applies here: h ₀ = λ _N / 4, where λ _{N is} the target wavelength to be suppressed.

A complete period P of the diffraction component in the period running direction R initially includes the four descending diffraction structure levels N ₁ to N ₄ and then two subsequent, again ascending diffraction structure levels N ₅ , N ₆ , where a structure depth of the diffraction structure level N ₅ of the diffraction structure level N ₃ and a structure depth of the diffraction structure level N ₆ those of the diffraction structure level N ₂ corresponds.

Based on 38 and 39 further explanations of optical diffraction components are given below 94 , 95 described for the suppression of at least one target wavelength by destructive interference. Components and functions corresponding to those described above with reference to the 1 to 37 and in particular with reference to the 36 and 37 have already been explained, have the same reference numerals and are not discussed again in detail.

The diffraction component 94 after 38 has diffraction structure levels following one another within a grating period P along a period running direction R N ₁ with structure depth 0, N ₂ with structure depth h ₁ , N ₃ with structure depth h ₁ + h ₂ and N ₄ with structure depth h ₂ . The following applies: h ₁ <h ₂ .

At the diffraction component 95 after 39 a diffraction structure level follow one another along the period running direction R within a period P N ₁ with structure depth 0, a diffraction structure level N ₂ with structure depth h ₁ , a diffraction structure level N ₃ with structure depth h ₂ and a diffraction structure level N ₄ with structure depth h ₁ + h ₂ . The following also applies here: h ₁ <h ₂ .

λ₁ und λ₂ sind dabei die beiden Ziel-Wellenlängen, die durch destruktive Interferenz mit den Beugungskomponenten 94 bzw. 95 unterdrückt werden sollen. Es gilt: h₁ = λ₁ / 4 und h₂ = λ₂/4.An intensity in the zeroth diffraction order can be based on the above in connection with 36 can be given as: $$\text{I.}\left(0\right)={\left|1+\text{exp}\left(i\pi \frac{{\lambda }_1}{\lambda }\right)+\text{exp}\left(i\pi \frac{{\lambda }_2}{\lambda }\right)+\text{exp}\left(i\pi \frac{{\lambda }_1+{\mathrm{<figure-callout\; id="2"\; label="\lambda "\; filenames="DE102019210450A1\_0010.png,DE102019210450A1\_0011.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_2}{\lambda }\right)\right|}^2$$

λ ₁ and λ ₂ are the two target wavelengths caused by destructive interference with the diffraction components 94 or. 95 should be suppressed. The following applies: h ₁ = λ _1/4 and h ₂ = λ _2/4.

For λ = λ ₁ and also for λ = λ _{2, the} following applies: I (0) = 0. These two wavelengths are therefore optimally suppressed.

Such a multi-stage grating in the manner of the grating of the embodiments 35 to 39 can be generalized to the suppression of a number n of target wavelengths by destructive interference. So that n-wavelengths are suppressed, 2n different diffraction structure levels N _i with the following heights are required: h ₁ , h ₂ , ... h _n , 0, h ₁ + h ₂ , h ₁ + h ₃ , ..., h ₁ + h _n , where the various structure depths h ₁ to h _n satisfy the following relationships: $${\text{<figure-callout id="1" label="H" filenames="DE102019210450A1\_0015.png,DE102019210450A1\_0026.png" state="{{state}}">H</figure-callout>}}_{\text{1}}<{\text{H}}_{\text{i}}<{\text{H}}_{\text{i + 1}}<{\text{<figure-callout id="1" label="2h" filenames="DE102019210450A1\_0015.png,DE102019210450A1\_0026.png" state="{{state}}">2h</figure-callout>}}_{\text{1}}$$

With the above-described optical diffraction components, alternatively or additionally, for example, target wavelengths suppressed in the infrared wavelength range, wavelengths in other wavelength ranges can also be suppressed, for example in the range of DUV wavelengths.

40 shows in a diagram a wavelength-dependent reflectivity R of a variant of the optical diffraction component with two structure depths d ₁ and d ₂ , for example in the manner of the optical grating 60 , 64 or 71 after the 16 , 19th and 22nd . The structure depths are: d ₁ = 45 nm and d ₂ = 52 nm. The result is one in the 40 solid reflectivity curve 96 . In addition, reflectivity curves are shown in dashed lines 97 and 98 for corresponding optical gratings with exactly one diffraction grating, designed with a structure depth d ₁ (reflectivity curve 97 ) and d ₂ (reflectivity curve 98 ).

The reflectivity curve 96 shows a suppression for the two target wavelengths λ ₁ ≈ 180 nm and λ ₂ ≈ 210 nm.

The following applies to the difference between these two target wavelengths λ ₁ , λ ₂ : $${\left({\mathrm{\lambda }}_1-{\mathrm{\lambda }}_2\right)}^2/{\left({\mathrm{<figure-callout\; id="1"\; label="\lambda "\; filenames="DE102019210450A1\_0015.png,DE102019210450A1\_0026.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_1+{\mathrm{\lambda }}_2\right)}^2=0.006$$

The suppression at these two DUV wavelengths is better than 10 ^-5 .

41 FIG. 13 shows the reflectivity R of an embodiment of a diffractive optical component of the type shown in FIG 14th to 22nd or. 25th to 32 , in this case designed as a superposition of a total of four diffraction gratings with different structure depths d ₁ to d ₄ . The following applies: d ₁ = 45 nm, d ₂ = 2 nm, d ₃ = 2.55 µm and d ₄ = 2.65 µm.

A wavelength-dependent reflectivity curve 97 that are in the 41 shows, corresponding to the structure depths d ₃ and d _4, two reflectivity minima with a suppression of better 10 ^-6 at λ ₃ = 10.2 μm and at λ ₄ = 10.6 μm.

In addition, corresponding to the two structure depths d ₁ and d ₂ , the grating with the reflectivity curve suppresses 97 also the two DUV wavelengths λ ₁ ≈ equal to 180 nm and λ ₂ ≈ equal to 210 nm with a suppression of better than 10 ^-6 , like the enlarged section of the 42 shows in the DUV area.

43 shows in a diagram how, when using an optical diffraction component composed of several diffraction structure groups, the requirements for a structure depth or slope tolerance relax with an increasing number of diffraction structure groups. Again, a reflectivity is shown as a function of a wavelength in the range between 10.0 and 11.0 μm. A target wavelength in the range of 10.6 µm should be suppressed with a suppression of better than 10 ^-4 .

At 98 is in the 43 a reflectivity curve for an optical diffraction component with exactly one diffraction structure group, i.e. with exactly one diffraction grating, is assumed for a structure depth d of 2.65 µm, which may fluctuate within a tolerance range of 0.5%.

At 99 a reflectivity curve is given for an optical diffraction component with two diffraction gratings as diffraction structure groups, which have the same structure depths d ₁ = d ₂ of 2.65 µm each and for which a tenfold tolerance range of 5% is permitted. The reflectivity curve results in the range of the target wavelength 99 a suppression that is better than the reflectivity curve despite the ten times higher tolerance bandwidth 98 .

At 100 is in the 43 a reflectivity curve for an optical diffraction component with two diffraction gratings is given as diffraction structure groups, the structure depths of which differ (d ₁ = 2.65 μm, d ₂ = 2.55 μm), a tolerance range of 3.5% being permitted in each case . At the target wavelength of 10.6 µm, there is a suppression that is that of the reflectivity curve 99 corresponds.

At 101 is in the 43 a reflectivity curve for an optical diffraction component with three diffraction structure groups in the form of three diffraction gratings with the same structure depth d ₁ = d ₂ = d ₃ of 2.65 μm and a tolerance range of 12% for the structure depth is given.

Due to the increasing suppression effects of the three diffraction gratings in the range of the target wavelength, this very high tolerance bandwidth in turn results in a very good suppression that meets the requirements of “suppression better than 10 ^-4 ”.

44 shows the optical grating again 60 with the diffraction structure levels N ₁ to N ₄ , as above in particular based on the 14th to 16 explained. In addition, the 44 two lithographic mask structures 105 , 106 shown in a lithographic production of the optical grating 60 can be used.

The ones in the 44 the optical grating 60 next adjacent illustrated lithographic mask structure 105 has mask areas 107 that are impermeable to an etching medium, as well as intermediate mask gaps 108 that are permeable to the etching medium. A periodicity of the mask structure 105 corresponds to that of the diffraction grating 62 after 15th . The mask structure 105 defines level slopes N ₄ / N ₃ between the diffraction structure levels N ₄ and N ₃ on the one hand and N ₁ / N ₂ between the diffraction structure levels N ₁ and N ₂ on the other hand.

For this purpose, the second lithographic mask structure is arranged offset along the period running direction x 106 with mask areas 109 and mask gaps 110 . A periodicity of this second lithographic mask structure 106 corresponds to that of the diffraction grating 61 after 14th . The second lithographic mask structure 106 defines the position of the level flanks N ₃ / N ₁ between the diffraction structure levels N ₃ and N ₁ on the one hand and N ₂ / N ₄ between the diffraction structure levels N ₂ and N ₄ on the other hand.

A topography of the diffraction structure levels N ₁ to N ₄ of the optical grating 60 can be described as the superposition of two binary structures, namely the one with the aid of the lithographic mask structures 105 , 106 diffraction structure groups that can be produced 61 , 62 (cf. also 14th and 15th ). Any of these binary structures 61 , 62 has first surface sections with a first structure depth, namely the positive structures 61 _P , 62 _{P of} the structural groups 61 , 62 , and second surface sections with a second structure depth, namely the negative structures 61 _N , 62 _N , which alternate with the first surface sections 61 _P , 62 _P along the period running direction x. Boundary areas between these adjacent surface sections 61 _P / 61 _N on the one hand and 62 _P / 62 _N on the other hand, that is to say the level edges N _i / N _j explained above, each of the binary structures 61 , 62 have perpendicular to the direction of the period and perpendicular to the plane of the drawing 14th to 16 and 44 a linear course. These boundary areas N ₃ / N ₁ , N ₂ / N _{4 of} the first binary structure 61 and the boundary regions N ₄ / N ₃ , N ₁ / N _{2 of} the second binary structure 62 run completely separate from one another, so do not overlap one another in their course perpendicular to the period running direction x.

Another characteristic of the optical grating 60 is that seen along the period running direction x, each rising level flank, i.e. N ₃ / N ₁ on the one hand and N ₄ / N ₃ on the other, is assigned a falling level flank of the same structure depth. The rising level edge N ₃ / N ₁ is assigned the falling level edge N ₂ / N ₄ . The rising level edge N ₄ / N ₃ is assigned the falling level edge N ₁ / N ₂ . The level flanks N ₃ / N ₁ and N ₂ / N ₄ assigned on the one hand have the structure depth d _1. The level flanks N ₄ / N ₃ and N ₁ / N ₂ also assigned to one another have the structure depth d ₂ .

45 shows the relationships in a lithographic production of the optical grating 64 (see also the 17th to 19th ). Components and functions corresponding to those described above with reference to the 1 to 44 and in particular with reference to the 14th to 19th and 44 have already been explained have the same reference numerals and will not be discussed again in detail.

For the optical grating 64 are in the 45 two lithographic mask structures 111 , 112 shown, which in turn have periodically consecutive mask areas and mask gaps. The lithographic mask structure 111 has mask areas 113 and mask gaps 114 and the lithographic mask structure 112 has mask areas 115 and mask gaps 116 .

During the lithographic production of the optical grating 64 defines the lithographic mask structure 111 the level flanks N ₃ / N ₂ on the one hand and N ₂ / N ₃ on the other hand and the further lithographic mask structure 112 defines the level edges N ₂ / N ₁ on the one hand and N ₁ / N ₂ on the other. Here, too, the optical grating results 64 as a superposition of two binary structures 65 , 66 (see. 17th and 18th ), whose boundary areas, i.e. the level edges N _i / N _j , perpendicular to the period running direction x and perpendicular to the plane of the drawing 17th to 19th and 45 run completely separately, so do not overlap.

Here, too, it applies again that, viewed along the direction of the cycle x, each rising level edge, i.e. the edges N ₂ / N ₁ and N ₃ / N ₂ , is in turn assigned a falling level edge of the same structure depth, namely the rising level edge N ₂ / N ₁ the falling level edge N ₁ / N ₂ and the rising level edge N ₃ / N ₂ the falling level edge N ₂ / N ₃ .

Also the optical grids 71 , 76 , 80 , which above in particular with reference to the 20th to 22nd , 25th to 28 as well as 29 to 32 can be described as a corresponding superimposition of binary structures whose boundary areas between the surface sections, that is to say their level edges N _i / N _j, do not overlap, as above with reference to the optical grating 60 and 64 already explained. In the case of the optical grating 76 and 80 these can be described as the superposition of three binary structures whose boundary areas, i.e. level edges N _i , N _j, do not overlap. Also for this grid 71 , 76 , 80 it is true that each rising level edge, seen along the period running direction x, is assigned a falling level edge of the same structure depth.

In the case of the above-described optical diffraction components with period directions of the diffraction structure groups that are not parallel to one another, there is a crossing of the level flanks, that is to say the boundary areas between the different surface sections of the diffraction structures. In this case, too, these boundary areas only overlap one another at points, that is to say at the highest longitudinal sections of the linear course of the level flanks, namely where they intersect.

Based on 46 is another embodiment of a diffractive optical component 117 , again in the form of an optical grating, for suppressing at least one target wavelength due to destructive interference. Components and functions corresponding to those described above with reference to the 1 to 45 have already been explained, have the same reference numerals and are not discussed again in detail.

The optical grating 117 is designed as a periodic grating structure profile with diffraction structures along the period direction x, the three diffraction structure levels N ₁ , N ₂ , N ₃ exhibit.

The mean diffraction structure level N ₂ specifies a reference height of 0 (d = 0) and is therefore also referred to as the neutral diffraction structure level. The further diffraction structure level N ₁ Measured against the reference height, it has a structure depth of d = + λ / 4 and is therefore also referred to as the positive diffraction structure level. The third level of diffraction structure N ₃ Measured against the reference height has a structure depth of d = - λ / 4 and is therefore also referred to as the negative diffraction structure level.

The three diffraction structure levels N ₁ to N ₃ thus specify different structure depths relative to the reference plane d = 0.

A grating period p of the grating structure profile of the optical grating 117 is in a total of 4 periods of the diffraction structure levels N ₁ to N ₃ divided. Two of these four periods are considered to be the neutral diffraction structure level N ₂ carried out, one of the four period segments as the positive diffraction structure level N ₁ and the fourth of the four periods is considered to be the negative diffraction structure level N ₃ executed. The sequence along the 46 selected unit cell, which is framed by a dashed line, is in the period running direction x: N ₂ , N ₁ , N ₂ , N ₃ .

Along the direction of the period x, the four period segments within a grating period p have the same structure length x _N.

Alternatively, it is also possible that the lengths of the period segments, that is to say the x extensions of the respective diffraction structure levels N ₁ to N ₃ , differ from each other in pairs. As a secondary condition for the lengths x _{Ni of} the period segments of the diffraction structure levels N ₁ to N ₃ should then be fulfilled: $${\text{x}}_{\text{N1}}+{\text{x}}_{\text{N1}}=2{\text{x}}_{\text{N2}}$$

The sum of the extents of the levels deviating from the neutral diffraction structure level should therefore be, as a good approximation, equal to twice the extent of the neutral diffraction structure level.

The described arrangement, i.e. the structure depths and the lengths along the direction of the period x, of the diffraction structure levels N ₁ to N ₃ is such that a first target wavelength λ ₁ in the infrared wavelength range, which is diffracted by the grating structure profile, has radiation components with three different phases that interfere with each other destructively in the zeroth diffraction order of the first target wavelength λ ₁ . There is thus a suppression effect, as above, inter alia, in connection with the other optical diffraction components according to the 1 to 45 was explained. As a theoretical consideration shows, this suppression effect is squared in comparison with the suppression of a single binary grating, not shown, so that the optical grating 117 has a suppression effect of, for example, 10 ^-4 if a binary grating at which instead of the negative diffraction structure levels N ₃ again positive diffraction structure levels N ₁ would have a suppression of 10 ^-2 .

The target wavelength can again be in the range between 10 µm and 11 µm.

Based on 47 and 48 the influence of a structure depth error on the diffraction efficiency is explained below. Here, it is assumed that light with the wavelength λ to be suppressed has a perpendicular incidence in the 47 and 48 from above onto the optical grating 117 occurs. This “vertical incidence” assumption serves only as a model assumption for the following consideration. In practice, the angle of incidence of the light regularly deviates from the perpendicular incidence. The structure depths of the optical diffraction components described here are then correspondingly adapted to the respective angle of incidence. The methods for performing this design adaptation are known to the person skilled in the art. In practice, the angles of incidence of the light vary with the wavelength to be suppressed, and thus also the structural depths of the optical diffraction component via the EUV collector. With an EUV collector 24 With a rotationally symmetrical design, a structure depth of the diffraction structure groups can be continuous from a center of the EUV collector 24 towards the edge of the EUV collector 24 vary.

With filled dots are in the 47 and 48 Areas of the same phase P _{0 of} the wave of reflected light are shown. Because the diffraction structure levels N ₁ on the one hand and N ₃ on the other hand, by an optical path length of λ / 4 compared to the neutral diffraction structure level N ₂ are offset, the result is that in the total of four period segments the in the 47 shown grating period of the optical Grid 117 In each case two areas of the reflected light result, the phase Po of which is reflected exactly half a wavelength, i.e. offset by λ / 2 compared to two other areas, which in the case of the perfect λ / 4 structure depths 47 leads to the perfect suppression of the incident light, i.e. to the destructive interference of the reflected light.

47 shows the case where the positive diffraction structure level N ₁ has a structure depth greater than λ / 4 and the negative diffraction structure level N ₃ has a structure depth which has the same absolute value as the structure depth of the positive diffraction structure level N ₁ , is accordingly also absolutely larger than λ / 4. With the grating after 47 so there is an altitude error.

Areas of the same phase P _{0, i.e.} of light from the positive diffractive structure level N ₁ on the one hand and from the negative diffraction structure level N ₃ on the other hand is reflected are in the 48 represented by open circles.

Like the comparison of the positions in the beam direction of the reflected light of these two phases P _{0, i.e.} those of the levels N ₁ or. N ₃ are reflected, with the corresponding phase positions Po in the perfect suppression situation 47 shows, lie behind in the situation 48 these two phases P _{0, i.e.} shifted by the correct phase position upwards or downwards by the same distance, so that an average value of the two shifted phases P _{0, i.e.} back to the position of the perfect phase position 47 comes to rest. This averaging effects an improvement in the suppression in the grating with the three diffraction structure levels N ₁ to N ₃ compared to a binary grating with only two diffraction structure levels corresponding to the diffraction structure levels N ₁ and N ₂ and corresponding height error.

49 shows a further variant of an optical diffraction component for suppressing at least one target wavelength in the form of an optical grating 118 with diffraction structures, again having three diffraction structure levels N ₁ , N ₂ and N ₃ . Components and functions corresponding to those described above with reference to the 1 to 48 and in particular with reference to the 46 to 48 have already been explained, have the same reference numerals and are not discussed again in detail.

Is shown in the 49 in turn, a unit cell, which extends along the direction of the period x over a period p, in dashed lines. The neutral diffraction structure level N ₂ , which is initially present in this unit cell in the period running direction x, has twice the length 2x _N compared to the two other diffraction structure levels. The sequence of the diffraction structure levels in the direction of the period within the unit cell shown is therefore: Neutral diffraction structure level N ₂ double length 2x _N , positive diffraction structure level N ₁ with single length x _N , negative diffraction structure level with single length x _N. With the optical grating 118 thus follows a positive diffraction structure level within the unit cell N ₁ directly a negative diffraction structure level N ₂ so that an intermediate level flank has a structure depth of λ / 2.

50 shows another embodiment of an optical grating 120 designed optical diffraction component to suppress at least one target wavelength, again with diffraction structures having four diffraction structure levels N ₁ to N ₄ . Components and functions corresponding to those described above with reference to the 1 to 49 and in particular with reference to the 46 to 49 have already been explained, have the same reference numerals and are not discussed again in detail. The optical grating has the direction of the period 120 the following sequence of diffraction structure levels: positive diffraction structure level N ₁ with structure depth + λ / 4, neutral diffraction structure level N ₂ , Negative diffraction structure level N ₃ with structure depth - λ / 4, double negative diffraction structure level N ₄ with structure depth - λ / 2, negative diffraction structure level N ₃ and neutral diffraction structure level N ₂ . The unit cell of the optical grating 120 thus includes the diffraction structure-level sequence N ₁ , N ₂ , N ₃ , N ₄ , N ₃ , N ₂ or a corresponding cyclical exchange.

• - λ / 4, Doppelt-Negativ-Beugungsstruktur-Niveau N₄ mit Strukturtiefe
• - λ / 2, Dreifach-Negativ-Beugungsstruktur-Niveau N₅ mit Strukturtiefe
• - 3 λ / 4, Doppelt-Negativ-Beugungsstruktur-Niveau N₄ mit Strukturtiefe
• - λ / 2, Negativ-Beugungsstruktur-Niveau N₃ mit Strukturtiefe - λ /4, und Neutral-Beugungsstruktur-Niveau N₂ . Die Einheitszelle des optischen Gitters 120 beinhaltet also die Beugungsstruktur-Niveau-Abfolge N₁ , N₂ , N₃ , N₄ , N₅ , N₄ , N₃ , N₂ oder eine entsprechende zyklische Vertauschung.

51 shows another embodiment of an optical grating 121 designed optical diffraction component for suppressing at least one target wavelength, again with diffraction structures having five diffraction structure levels N ₁ to N ₅ . Components and functions corresponding to those described above with reference to the 1 to 50 and in particular with reference to the 46 to 50 have already been explained, have the same reference numerals and are not discussed again in detail. The optical grating has the direction of the period 121 the following sequence of diffraction structure levels: positive diffraction structure level N ₁ with structure depth + λ / 4, neutral diffraction structure level N ₂ , Negative diffraction structure level N ₃ with structure depth

• - λ / 4, double negative diffraction structure level N ₄ with structure depth
• - λ / 2, triple negative diffraction structure level N ₅ with structure depth
• - 3 λ / 4, double negative diffraction structure level N ₄ with structure depth
• - λ / 2, negative diffraction structure level N ₃ with structure depth - λ / 4, and neutral diffraction structure level N ₂ . The unit cell of the optical grating 120 thus includes the diffraction structure-level sequence N ₁ , N ₂ , N ₃ , N ₄ , N ₅ , N ₄ , N ₃ , N ₂ or a corresponding cyclical exchange.

The additional diffraction structure levels N ₄ with the optical grating 120 or. N ₄ , N ₅ with the optical grating 121 lead to an additional increase in the diffraction effect, i.e. to a further increase in the destructive interference of the target wavelength λ.

The above-explained structuring of the optical grating can cause the EUV collector 24 reflected stray light radiation, for example, with an infrared wavelength in a zero order destructively interferes and thus a stray light intensity in the zero order is suppressed. The optical diffraction components described above are usually used as reflective components.

A basic body of the EUV collector 24 can be made of aluminum. Alternative materials for this base body are copper, alloys with the constituent copper and / or aluminum or alloys of copper and aluminum oxide or silicon produced by powder metallurgy.

The projection exposure system is used to produce a micro- or nano-structured component 1 used as follows: First, the reflection mask 10 or the reticle and the substrate or the wafer 11 provided. A structure is then created on the reticle 10 onto a photosensitive layer of the wafer 11 using the projection exposure system 1 projected. A micro- or nanostructure is then created on the wafer by developing the light-sensitive layer 11 and thus the microstructured component is generated.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2017/207401 A1 [0002]
• WO 2014/114405 A2 [0002]
• EP 1540423 B1 [0002]
• US 2014/0131586 A1 [0002]
• DE 102009044462 A1 [0002]
• DE 102009045096 A1 [0061]
• DE 102012202675 A1 [0062]

Non-patent literature cited

• T. Feigl et al., 2016 EUVL Workshop, Berkeley, June 13-16, 2016 [0002]
• M. Oliva et al., OPTICS EXPRESS, Vol. 19, No. 15, 2011, pp. 1473 to 1475 [0002]
• M. Oliva et al., OPTICS LETTERS Vol. 35, No. 16, 2010, pp. 2774 to 2776 describe different variants of blaze grids. From the specialist article "Diffractive elements designed to suppress unwanted zeroth order due to surface depth error" by V. Kettunen et al., Journal of Modern Optics 51, 14, 2111-2123, 2004 [0002]

Claims (20)

Optical diffraction component (34; 46; 47; 57; 58; 59; 60; 64; 71; 76; 80; 86; 91; 92; 93; 94; 95; 117; 118; 119; 120; 121) for suppression at least a target wavelength (λ _N ) due to destructive interference, - with at least three diffraction structure levels (N _i ), which specify different structure depths (d _i ) relative to a reference plane, - the three diffraction structure levels (N _i ) at least two Diffraction structural groups (35, 36; 61, 62; 65, 66; 72, 73; 77, 78, 79; 81, 82, 83; 87, 88, 89; N1, N2; N2, N3; N3, N1; N _n , N _n +1) can be assigned, - a first of the diffraction structure groups (35; 61; 65; 72; 77; 81; 87; N _n , N _n +1) for suppressing a first target wavelength λ ₁ in the zeroth diffraction order and - wherein a second of the diffraction structure groups (36; 62; 66; 73; 78; 82; 88; N _n +1, N _n +2) for suppressing a second target wavelength λ ₂ in the zeroth diffraction order is executed, - where for the two target wavelengths λ ₁ and λ ₂ applies: (λ ₁ - λ ₂ ) ² / (λ ₁ + λ ₂ ) ² <20%, - where a topography of the diffraction structure levels (Ni) can be described as a superposition of two binary diffraction structure groups (35, 36; 61, 62; 65, 66; 72, 73; 77, 78, 79; 81, 82, 83; 87, 88, 89) - each of the binary diffraction structure groups having: - first surface sections (61 _P ; 62 _P ) with a first structure depth; - second surface sections (61 _N ; 62 _N ) with a second structure depth which alternate along a running direction (x) with the first surface sections (61 _P , 61 _N ), - where border areas (N ₃ / N ₁ , N ₂ / N ₄ , N ₄ / N ₃ , N ₁ / N ₂ ) between adjacent surface sections (61 _P , 61 _N ; 62 _P , 62 _N ) of each of the binary diffraction structure groups (35, 36; 61, 62; 65, 66; 72, 73; 77, 78, 79; 81, 82, 83; 87, 88, 89; N1, N2; N2, N3; N3, N1; N _n , N _n + 1) have a linear course, where - first boundary regions (N ₃ / N ₁ , N ₂ / N ₄ ) of the first of the two binary diffraction structure groups (35, 36; 61, 62; 65, 66; 72, 73; 77, 78, 79; 81, 82, 83; 87, 88, 89; N1, N2; N2, N3; N3, N1; N _n N _n +1) and - second limit areas (N ₄ / N ₃ , N ₁ / N ₂ ) of the second of the two binary ones Diffraction structural groups (35, 36; 61, 62; 65, 66; 72, 73; 77, 78, 79; 81, 82, 83; 87, 88, 89; N1, N2; N2, N3; N3, N1; N _n , N _n +1) - superimposed on each other at most along sections of their linear course n. Optical diffraction component after Claim 1 , characterized in that the first boundary regions (N ₃ / N ₁ , N ₂ / N ₄ ) of the first of the two binary diffraction structure groups (61, 62; 65, 66; 72, 73; 77, 78, 79; 81, 82, 83; 87, 88, 89; N1, N2; N2, N3; N3, N1; Nn, N _n +1) and the second boundary areas (N ₄ / N ₃ , N ₁ / N ₂ ) of the second of the two binary diffraction structural groups (61, 62; 65, 66; 72, 73; 77, 78, 79; 81, 82, 83; 87, 88, 89; N1, N2, N2, N3; N3, N1; Nn, N _n +1) run completely separate from each other. Optical diffraction component after Claim 1 or 2 , characterized in that a first of the diffraction structure groups (35; 61; 65; 72; 77; 81; 87) is designed as the first diffraction grating arranged on a grating surface (33), - with a first grating period (ph; p ₁ ) - with a first structure depth (ie; d ₁ ), measured as the optical path difference between first diffraction positive structures (37) and first diffraction negative structures (38) perpendicular to one of these first structures (37, 38) respectively surrounding surface section of the grating surface (33), - a second of the diffraction structure groups (36; 62; 66; 73; 78; 82; 88) being designed as a second diffraction grating arranged on the grating surface (33), - with a second grating period (pv; p ₂ ), - with a second structure depth (dv; d ₂ ), measured as the optical path difference between second diffraction positive structures (40) and second diffraction negative structures (41) perpendicular to one of these second structures (40, 41) respectively surrounding surface section the gitte surface (33). Optical diffraction component after Claim 3 , characterized in that - the first grating period (ph) runs along a first period running direction (39) of the first diffraction grating (35), - the second grating period (pv) runs along a second period running direction (42) of the second diffraction grating (36) ) runs, - the two period running directions (39, 42) not running parallel to one another. Optical diffraction component according to one of the Claims 3 or 4th , characterized by at least one further diffraction grating (48) arranged on the grating surface (33), with further diffraction positive structures (49) and further diffraction negative structures (50), with an area ratio of areas of the further diffraction positive structures (49) Areas of the other negative diffraction structures (50) in the range between 0.9 and 1.1, with a further grating period (pd), - with a further structure depth (dd), measured as the optical path difference between the further diffraction positive structures (49) and the further diffraction negative structures (50) perpendicular to one of these further structures (49, 50) each surrounding surface section of the grid surface (33). Optical diffraction component after Claim 5 , characterized by - a ratio (pd / dd) between the further grating period (pd) and the further structure depth (dd), which is greater than 10, and / or - by a period ratio (ph / pd) of the first grating period (ph) to the further grating period (pd) in the range between 0.9 and 1.1, and / or, - that - the first grating period (ph) runs along a first period running direction (39) of the first diffraction grating (35), - the further grating period (pd) runs along a further period running direction (51) of the further diffraction grating (48), - the two period running directions (39, 51) not running parallel to one another. Optical diffraction component according to one of the Claims 1 to 6th , characterized in that the surfaces of the diffraction positive structures (37, 40, 49) and the diffraction negative structures (38, 41, 50) of the different diffraction structure groups (35, 36, 48) make equal contributions to the entire grating surface (33) deliver. Optical diffraction component (117; 118; 119; 120; 121) - with a periodic grating structure profile with diffraction structures, having three diffraction structure levels (N ₁ to N ₃ ; N ₁ to N ₄ , N ₁ to N ₅ ), - which specify different structure depths relative to a reference plane, - the arrangement of the diffraction structures is such that a wavelength range around a first target wavelength λ ₁ in the infrared wavelength range, which is diffracted by the grating structure profile, radiation components with at least three different Has phases which destructively interfere with one another at least in the zeroth and / or +/- first diffraction order of the first target wavelength λ ₁ , - the diffraction structure levels (N ₁ to N ₃ ; N ₁ to N ₄ , N ₁ to N ₅ ) specify a topography of a grating period of the grating structure profile that is regularly repeated along a period running direction, - the diffraction structure levels (N ₁ to N ₃ ; N ₁ to N ₄ , N ₁ to N ₅ ) a Have: - a neutral diffraction structure level (N ₂ ), which corresponds to a reference height of zero, - a positive diffraction structure level (N ₁ ), which compared to the neutral diffraction structure level by an optical path length of λ ₁ / 4 +/- 20% higher, and - a negative diffraction structure level (N ₃ ; N _3, N _4, N _3, N _4, N _5), which is located lower with respect to the neutral diffraction structure level by an optical path length of λ _1/4 +/- 20%. Optical diffraction component after Claim 8 , characterized in that a grating period of the grating structure profile is divided into four period segments of the diffraction structure levels, two of the four period segments being designed as neutral diffraction structure segments with the neutral diffraction structure level (N ₂ ), one of the four period segments being positive Diffraction structure section (N ₁ ) is designed with the positive diffraction structure level and one of the four period sections is designed as a negative diffraction structure section (N ₃ ) with the negative diffraction structure level. Optical diffraction component after Claim 9 , characterized in that the four period segments along the period running direction (x) have the same length (x _N ) +/- 20%. Optical diffraction component after Claim 9 or 10 , characterized by the following sequence of the four periods: positive diffraction structure level (N ₁ ), neutral diffraction structure level (N ₂ ), negative diffraction structure level (N ₃ ), neutral diffraction structure level (N ₂ ). Optical diffraction component according to one of the Claims 8 to 11 , characterized in that the arrangement of the diffraction structures is such that a target wavelength range, containing the first target wavelength λ ₁ , in the infrared wavelength range diffracted by the grating structure profile has radiation components with at least three different phases which destructively interfere with each other at least in the zeroth and / or +/- first diffraction order of the first target wavelength λ ₁ , with one of these in the target wavelength range in addition to the first target wavelength λ ₁ different second target wavelength λ ₂ , the arrangement of the diffraction structures is such that a wavelength range around the second target wavelength λ ₂ in the infrared wavelength range, which is diffracted by the grating structure profile, radiation components with at least three different phases which interfere with each other destructively at least in the zeroth and / or +/- first diffraction order of the second target wavelength λ ₂ , with the following applies for the two target wavelengths λ ₁ and λ ₂ : (λ ₁ - λ ₂ ) ² / ( λ ₁ + λ ₂ ) ² <20%. EUV collector (24) for use in an EUV projection exposure system with an optical diffraction component (34; 46; 47; 57; 58; 59; 60; 64; 71; 76; 80; 86; 91; 92; 93; 94; 94; 95; 117; 118; 119; 120; 121) according to one of the Claims 1 to 12 . EUV collector after Claim 13 , characterized in that the collector mirror is designed such that it guides EUV radiation (3) to a focal region (26), the optical diffraction component being designed such that it removes the radiation (30) of the at least one target wavelength from the focal area (26) leads. Lighting system with an EUV collector (24) Claim 13 or 14th and with illumination optics (6) for illuminating an object field (4) in which an object (10) to be imaged can be arranged, with EUV useful light as illumination light (3). Optical system with a lighting system according to Claim 15 and with projection optics (7) for imaging the object field (4) in an image field (8) in which a substrate (11) can be arranged, onto which a section of the object (10) to be imaged is to be imaged. Projection exposure system (1) with an optical system Claim 16 and with an EUV light source (2). Projection exposure system (1) according to Claim 17 , characterized in that the EUV light source (2) has a pump light source for generating a plasma generating EUV wavelengths, the pump light source being designed for generating a prepulse with a prepulse light wavelength and for generating a main pulse with a main pulse light wavelength, wherein the pre-pulsed light wavelength differs from the main pulsed light wavelength. Method for producing a structured component with the following method steps: - providing a reticle (10) and a wafer (11), - projecting a structure on the reticle (10) onto a light-sensitive layer of the wafer (11) with the aid of the projection exposure system Claim 17 or 18th - Generating a micro- and / or nanostructure on the wafer (11). Structured component, manufactured using a process according to Claim 19 .

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